Engine system and method for efficient emission control device purging

ABSTRACT

Various systems and methods are disclosed for carrying out combustion in a fuel-cut operation in some or all of the engine cylinders of a vehicle. Further, various subsystems are considered, such as fuel vapor purging, air-fuel ratio control, engine torque control, catalyst design, and exhaust system design.

BACKGROUND AND SUMMARY

Engines are usually designed with the ability to deliver a peak output,although most engine operation is performed well below this peak value.As such, it can be beneficial to operate with some cylinders inductingair without fuel injection as described in U.S. Pat. No. 6,568,177.

As described in U.S. Pat. No. 6,568,177, periodically it may benecessary to purge stored NOx by operating all of the cylindersstoichiometric or rich.

The inventors herein have recognized that such an approach may result inwasting excess fuel in configurations where there are multiple cylinderbanks, each having an upstream emission control device, when it isdesired to reduce NOx stored in a downstream device. Specifically, fuelis must be used to reduce stored oxidants in both upstream devices,before downstream stored NOx can be reduced.

The above disadvantage can be overcome by a method for controlling anengine having at least a first and second group of cylinders. The methodcomprises:

operating the engine in a first mode wherein the first cylinder groupoperates with air and substantially no injected fuel and the secondcylinder group operates to combust air and injected fuel; and

transitioning the engine to operating in a second mode wherein both thefirst cylinder group and the second cylinder group operate to combustair and injected fuel, combustion in one of said first and secondcylinder group oscillating about stoichiometry and combustion in theother of said first and second cylinder group being rich ofstoichiometry

In this way, it is possible, in one embodiment, to provide the abilityto operate some cylinders without fuel injection, and save still furtherfuel when it may be desired to purge NOx stored in a downstream emissioncontrol device. Note, however, that the above approach can be used inother situations as well to improve performance.

In another aspect, another disadvantage with prior approaches can relateto transitioning from operation with some cylinder deactivated andactive cylinders combusting, to all cylinders combusting. Specifically,retarded ignition timing is used, along with throttling to reduce anytorque disturbance that may result. However, throttle is generally toslow due to manifold filling effects, and as such, ignition timingretard is heavily relied upon. Significant reliance on ignition timingretard, however, can result is degraded fuel economy.

Therefore, to overcome the above disadvantage, the inventors herein haverecognized that the above fuel economy degradation can be reduced byoperating the re-enabled cylinders at a lean combustion limit, therebyreducing the amount of ignition timing retard that may be needed. In oneexample, a method for controlling an engine having at least a first andsecond group of cylinders comprises:

operating the engine in a first mode wherein the first cylinder groupoperates with air and substantially no injected fuel and the secondcylinder group operates to combust air and injected fuel; and

transitioning the engine to operating in a second mode wherein both thefirst cylinder group and the second cylinder group operate to combustair and injected fuel, combustion in both said first and second cylindergroup being lean of stoichiometry at a lean combustion limit withretarded ignition timing.

BRIEF DESCRIPTION OF THE FIGURES

The above features and advantages will be readily apparent from thefollowing detailed description of example embodiment(s). Further, thesefeatures and advantages will also be apparent from the followingdrawings.

FIG. 1 is a block diagram of a vehicle illustrating various componentsof the powertrain system;

FIGS. 1A and 1B show a partial engine view;

FIGS. 2A-2T show various schematic system configurations;

FIGS. 3A1-3A2 are graphs representing different engine operating modesat different speed torque regions;

FIGS. 3B-3C, 4-5, 7-11, 12A-12B, 13A, 13C1-C2, and 16-20 and 34 are highlevel flow charts showing example routines and methods;

FIGS. 6A-D, 13B1-13B2 and 13D1-13D2 are graphs show example operation;

FIGS. 14 and 15 show a bifurcated catalyst;

FIG. 21 contains graphs showing a deceleration torque request beingclipped via a torque converter model to keep engine speed above aminimum allowed value;

FIGS. 22-27 show engine torque over an engine cycle during a transitionbetween different cylinder cut-out modes;

FIGS. 28-33 show Fourier diagrams of engine torque excitation acrossvarious frequencies for different operating modes, and whentransitioning between operating modes.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT(S) OF THE INVENTION

Referring to FIG. 1, internal combustion engine 10, further describedherein with particular reference to FIGS. 1A and 1B, is shown coupled totorque converter 11 via crankshaft 13. Torque converter 11 is alsocoupled to transmission 15 via turbine shaft 17. Torque converter 11 hasa bypass, or lock-up clutch 14 which can be engaged, disengaged, orpartially engaged. When the clutch is either disengaged or partiallyengaged, the torque converter is said to be in an unlocked state. Thelock-up clutch 14 can be actuated electrically, hydraulically, orelectro-hydraulically, for example. The lock-up clutch 14 receives acontrol signal (not shown) from the controller, described in more detailbelow. The control signal may be a pulse width modulated signal toengage, partially engage, and disengage, the clutch based on engine,vehicle, and/or transmission operating conditions. Turbine shaft 17 isalso known as transmission input shaft. Transmission 15 comprises anelectronically controlled transmission with a plurality of selectablediscrete gear ratios. Transmission 15 also comprises various othergears, such as, for example, a final drive ratio (not shown).Transmission 15 is also coupled to tire 19 via axle 21. Tire 19interfaces the vehicle (not shown) to the road 23. Note that in oneexample embodiment, this powertrain is coupled in a passenger vehiclethat travels on the road.

FIGS. 1A and 1B show one cylinder of a multi-cylinder engine, as well asthe intake and exhaust path connected to that cylinder. As describedlater herein with particular reference to FIG. 2, there are variousconfigurations of the cylinders and exhaust system, as well as variousconfiguration for the fuel vapor purging system and exhaust gas oxygensensor locations.

Continuing with FIG. 1A, direct injection spark ignited internalcombustion engine 10, comprising a plurality of combustion chambers, iscontrolled by electronic engine controller 12. Combustion chamber 30 ofengine 10 is shown including combustion chamber walls 32 with piston 36positioned therein and connected to crankshaft 40. A starter motor (notshown) is coupled to crankshaft 40 via a flywheel (not shown). In thisparticular example, piston 36 includes a recess or bowl (not shown) tohelp in forming stratified charges of air and fuel. Combustion chamber,or cylinder, 30 is shown communicating with intake manifold 44 andexhaust manifold 48 via respective intake valves 52 a and 52 b (notshown), and exhaust valves 54 a and 54 b (not shown). Fuel injector 66Ais shown directly coupled to combustion chamber 30 for deliveringinjected fuel directly therein in proportion to the pulse width ofsignal fpw received from controller 12 via conventional electronicdriver 68. Fuel is delivered to fuel injector 66A by a conventional highpressure fuel system (not shown) including a fuel tank, fuel pumps, anda fuel rail.

Intake manifold 44 is shown communicating with throttle body 58 viathrottle plate 62. In this particular example, throttle plate 62 iscoupled to electric motor 94 so that the position of throttle plate 62is controlled by controller 12 via electric motor 94. This configurationis commonly referred to as electronic throttle control (ETC), which isalso utilized during idle speed control. In an alternative embodiment(not shown), which is well known to those skilled in the art, a bypassair passageway is arranged in parallel with throttle plate 62 to controlinducted airflow during idle speed control via a throttle control valvepositioned within the air passageway.

Exhaust gas sensor 76 is shown coupled to exhaust manifold 48 upstreamof catalytic converter 70 (note that sensor 76 corresponds to variousdifferent sensors, depending on the exhaust configuration as describedbelow with regard to FIG. 2. Sensor 76 may be any of many known sensorsfor providing an indication of exhaust gas air/fuel ratio such as alinear oxygen sensor, a UEGO, a two-state oxygen sensor, an EGO, a HEGO,or an HC or CO sensor. In this particular example, sensor 76 is atwo-state oxygen sensor that provides signal EGO to controller 12 whichconverts signal EGO into two-state signal EGOS. A high voltage state ofsignal EGOS indicates exhaust gases are rich of stoichiometry and a lowvoltage state of signal EGOS indicates exhaust gases are lean ofstoichiometry. Signal EGOS is used to advantage during feedback air/fuelcontrol in a conventional manner to maintain average air/fuel atstoichiometry during the stoichiometric homogeneous mode of operation.

Conventional distributorless ignition system 88 provides ignition sparkto combustion chamber 30 via spark plug 92 in response to spark advancesignal SA from controller 12.

Controller 12 causes combustion chamber 30 to operate in either ahomogeneous air/fuel mode or a stratified air/fuel mode by controllinginjection timing. In the stratified mode, controller 12 activates fuelinjector 66A during the engine compression stroke so that fuel issprayed directly into the bowl of piston 36. Stratified air/fuel layersare thereby formed. The strata closest to the spark plug contain astoichiometric mixture or a mixture slightly rich of stoichiometry, andsubsequent strata contain progressively leaner mixtures. During thehomogeneous mode, controller 12 activates fuel injector 66A during theintake stroke so that a substantially homogeneous air/fuel mixture isformed when ignition power is supplied to spark plug 92 by ignitionsystem 88. Controller 12 controls the amount of fuel delivered by fuelinjector 66A so that the homogeneous air/fuel mixture in chamber 30 canbe selected to be at stoichiometry, a value rich of stoichiometry, or avalue lean of stoichiometry. The stratified air/fuel mixture will alwaysbe at a value lean of stoichiometry, the exact air/fuel being a functionof the amount of fuel delivered to combustion chamber 30. An additionalsplit mode of operation wherein additional fuel is injected during theexhaust stroke while operating in the stratified mode is also possible.

Nitrogen oxide (NOx) adsorbent or trap 72 is shown positioned downstreamof catalytic converter 70. NOx trap 72 is a three-way catalyst thatadsorbs NOx when engine 10 is operating lean of stoichiometry. Theadsorbed NOx is subsequently reacted with HC and CO and catalyzed whencontroller 12 causes engine 10 to operate in either a rich homogeneousmode or a near stoichiometric homogeneous mode such operation occursduring a NOx purge cycle when it is desired to purge stored NOx from NOxtrap 72, or during a vapor purge cycle to recover fuel vapors from fueltank 160 and fuel vapor storage canister 164 via purge control valve168, or during operating modes requiring more engine power, or duringoperation modes regulating temperature of the omission control devicessuch as catalyst 70 or NOx trap 72. (Again, note that emission controldevices 70 and 72 can correspond to various devices described in FIGS.2A-R). Also note that various types of purging systems can be used, asdescribed in more detail below with regard to FIGS. 2A-R.

Controller 12 is shown in FIG. 1A as a conventional microcomputer,including microprocessor unit 102, input/output ports 104, an electronicstorage medium for executable programs and calibration values shown asread only memory chip 106 in this particular example, random accessmemory 108, keep alive memory 110, and a conventional data bus.Controller 12 is shown receiving various signals from sensors coupled toengine 10, in addition to those signals previously discussed, includingmeasurement of inducted mass air flow (MAF) from mass air flow sensor100 coupled to throttle body 58; engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a profile ignitionpickup signal (PIP) from Hall effect sensor 118 coupled to crankshaft40; and throttle position TP from throttle position sensor 120; andabsolute Manifold Pressure Signal MAP from sensor 122. Engine speedsignal RPM is generated by controller 12 from signal PIP in aconventional manner and manifold pressure signal MAP from a manifoldpressure sensor provides an indication of vacuum, or pressure, in theintake manifold. During stoichiometric operation, this sensor can giveand indication of engine load. Further, this sensor, along with enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In a one example, sensor 118, which is also used as anengine speed sensor, produces a predetermined number of equally spacedpulses every revolution of the crankshaft.

In this particular example, temperature Tcat1 of catalytic converter 70and temperature Tcat2 of emission control device 72 (which can be a NOxtrap) are inferred from engine operation as disclosed in U.S. Pat. No.5,414,994, the specification of which is incorporated herein byreference. In an alternate embodiment, temperature Tcat1 is provided bytemperature sensor 124 and temperature Tcat2 is provided by temperaturesensor 126.

Continuing with FIG. 1A, camshaft 130 of engine 10 is showncommunicating with rocker arms 132 and 134 for actuating intake valves52 a, 52 b and exhaust valve 54 a, 54 b. Camshaft 130 is directlycoupled to housing 136. Housing 136 forms a toothed wheel having aplurality of teeth 138. Housing 136 is hydraulically coupled to an innershaft (not shown), which is in turn directly linked to camshaft 130 viaa timing chain (not shown). Therefore, housing 136 and camshaft 130rotate at a speed substantially equivalent to the inner camshaft. Theinner camshaft rotates at a constant speed ratio to crankshaft 40.However, by manipulation of the hydraulic coupling as will be describedlater herein, the relative position of camshaft 130 to crankshaft 40 canbe varied by hydraulic pressures in advance chamber 142 and retardchamber 144. By allowing high pressure hydraulic fluid to enter advancechamber 142, the relative relationship between camshaft 130 andcrankshaft 40 is advanced. Thus, intake valves 52 a, 52 b and exhaustvalves 54 a, 54 b open and close at a time earlier than normal relativeto crankshaft 40. Similarly, by allowing high pressure hydraulic fluidto enter retard chamber 144, the relative relationship between camshaft130 and crankshaft 40 is retarded. Thus, intake valves 52 a, 52 b, andexhaust valves 54 a, 54 b open and close at a time later than normalrelative to crankshaft 40.

Teeth 138, being coupled to housing 136 and camshaft 130, allow formeasurement of relative cam position via cam timing sensor 150 providingsignal VCT to controller 12. Teeth 1, 2, 3, and 4 are preferably usedfor measurement of cam timing and are equally spaced (for example, in aV-8 dual bank engine, spaced 90 degrees apart from one another) whiletooth 5 is preferably used for cylinder identification, as describedlater herein. In addition, controller 12 sends control signals (LACT,RACT) to conventional solenoid valves (not shown) to control the flow ofhydraulic fluid either into advance chamber 142, retard chamber 144, orneither.

Relative cam timing is measured using the method described in U.S. Pat.No. 5,548,995, which is incorporated herein by reference. In generalterms, the time, or rotation angle between the rising edge of the PIPsignal and receiving a signal from one of the plurality of teeth 138 onhousing 136 gives a measure of the relative cam timing. For theparticular example of a V-8 engine, with two cylinder banks and afive-toothed wheel, a measure of cam timing for a particular bank isreceived four times per revolution, with the extra signal used forcylinder identification.

Sensor 160 provides an indication of both oxygen concentration in theexhaust gas as well as NOx concentration. Signal 162 provides controllera voltage indicative of the O2 concentration while signal 164 provides avoltage indicative of NOx concentration. Alternatively, sensor 160 canbe a HEGO, UEGO, EGO, or other type of exhaust gas sensor. Also notethat, as described above with regard to sensor 76, sensor 160 cancorrespond to various different sensors depending on the systemconfiguration, as described in more detail below with regard to FIG. 2.

As described above, FIGS. 1A (and 1B) merely show one cylinder of amulti-cylinder engine, and that each cylinder has its own set ofintake/exhaust valves, fuel injectors, spark plugs, etc.

Referring now to FIG. 1B, a port fuel injection configuration is shownwhere fuel injector 66B is coupled to intake manifold 44, rather thandirectly cylinder 30.

Also, in the example embodiments described herein, the engine is coupledto a starter motor (not shown) for starting the engine. The startermotor is powered when the driver turns a key in the ignition switch onthe steering column, for example. The starter is disengaged after enginestart as evidence, for example, by engine 10 reaching a predeterminedspeed after a predetermined time. Further, in the disclosed embodiments,an exhaust gas recirculation (EGR) system routes a desired portion ofexhaust gas from exhaust manifold 48 to intake manifold 44 via an EGRvalve (not shown). Alternatively, a portion of combustion gases may beretained in the combustion chambers by controlling exhaust valve timing.

The engine 10 operates in various modes, including lean operation, richoperation, and “near stoichiometric” operation. “Near stoichiometric”operation refers to oscillatory operation around the stoichiometric airfuel ratio. Typically, this oscillatory operation is governed byfeedback from exhaust gas oxygen sensors. In this near stoichiometricoperating mode, the engine is operated within approximately one air-fuelratio of the stoichiometric air-fuel ratio. This oscillatory operationis typically on the order of 1 Hz, but can vary faster and slower than 1Hz. Further, the amplitude of the oscillations are typically within 1a/f ratio of stoichiometry, but can be greater than 1 a/f ratio undervarious operating conditions. Note that this oscillation does not haveto be symmetrical in amplitude or time. Further note that an air-fuelbias can be included, where the bias is adjusted slightly lean, or rich,of stoichiometry (e.g., within 1 a/f ratio of stoichiometry). Also notethat this bias and the lean and rich oscillations can be governed by anestimate of the amount of oxygen stored in upstream and/or downstreamthree way catalysts.

As described below, feedback air-fuel ratio control is used forproviding the near stoichiometric operation. Further, feedback fromexhaust gas oxygen sensors can be used for controlling air-fuel ratioduring lean and during rich operation. In particular, a switching type,heated exhaust gas oxygen sensor (HEGO) can be used for stoichiometricair-fuel ratio control by controlling fuel injected (or additional airvia throttle or VCT) based on feedback from the HEGO sensor and thedesired air-fuel ratio. Further, a UEGO sensor (which provides asubstantially linear output versus exhaust air-fuel ratio) can be usedfor controlling air-fuel ratio during lean, rich, and stoichiometricoperation. In this case, fuel injection (or additional air via throttleor VCT) is adjusted based on a desired air-fuel ratio and the air-fuelratio from the sensor. Further still, individual cylinder air-fuel ratiocontrol could be used, if desired.

Also note that various methods can be used to maintain the desiredtorque such as, for example, adjusting ignition timing, throttleposition, variable cam timing position, exhaust gas recirculationamount, and a number of cylinders carrying out combustion. Further,these variables can be individually adjusted for each cylinder tomaintain cylinder balance among all the cylinder groups.

Referring now to FIG. 2A, a first example configuration is describedusing a V-8 engine, although this is simply one example, since a V-10,V-12, 14, 16, etc., could also be used. Note that while numerous exhaustgas oxygen sensors are shown, a subset of these sensors can also beused. Further, only a subset of the emission control devices can beused, and a non-y-pipe configuration can also be used. As shown in FIG.2A, some cylinders of first combustion chamber group 210 are coupled tothe first catalytic converter 220, while the remainder are coupled tocatalyst 222. Upstream of catalyst 220 and downstream of the firstcylinder group 210 is an exhaust gas oxygen sensor 230. Downstream ofcatalyst 220 is a second exhaust gas sensor 232. In this example, groups210 and 212 each have four cylinders. However, either group 210 or group212 could be divided into other groups, such as per cylinder bank. Thiswould provide four cylinder groups (two on each bank, each with twocylinders in the group). In this way, two different cylinder groups canbe coupled to the same exhaust gas path on one side of the engine'sbank.

Similarly, some cylinders of second combustion chamber group 212 arecoupled to a second catalyst 222, while the remainder are coupled tocatalyst 220. Upstream and downstream are exhaust gas oxygen sensors 234and 236 respectively. Exhaust gas spilled from the first and secondcatalyst 220 and 222 merge in a Y-pipe configuration before enteringdownstream under body catalyst 224. Also, exhaust gas oxygen sensors 238and 240 are positioned upstream and downstream of catalyst 224,respectively.

In one example embodiment, catalysts 220 and 222 are platinum andrhodium catalysts that retain oxidants when operating lean and releaseand reduce the retained oxidants when operating rich. Further, thesecatalysts can have multiple bricks, and further these catalysts canrepresent several separate emission control devices.

Similarly, downstream underbody catalyst 224 also operates to retainoxidants when operating lean and release and reduce retained oxidantswhen operating rich. As described above, downstream catalyst 224 can bea group of bricks, or several emission control devices. Downstreamcatalyst 224 is typically a catalyst including a precious metal andalkaline earth and alkaline metal and base metal oxide. In thisparticular example, downstream catalyst 224 contains platinum andbarium.

Note that various other emission control devices could be used, such ascatalysts containing palladium or perovskites. Also, exhaust gas oxygensensors 230 to 240 can be sensors of various types. For example, theycan be linear oxygen sensors for providing an indication of air-fuelratio across a broad range. Also, they can be switching type exhaust gasoxygen sensors that provide a switch in sensor output at thestoichiometric point. Also, the system can provide less than all ofsensors 230 to 240, for example, only sensors 230, 234, and 240. Inanother example, only sensor 230, 234 are used with only devices 220 and222. Also, while FIG. 2A shows a V-8 engine, various other numbers ofcylinders could be used. For example, an 14 engine can be used, wherethere are two groups of two cylinders leading to a common exhaust pathwith and upstream and downstream emission control device.

When the system of FIG. 2A is operated in an AIR/LEAN mode, firstcombustion group 210 is operated at a lean air-fuel ratio (typicallyleaner than about 18:1) and second combustion group 212 is operatedwithout fuel injection. Thus, in this case, and during this operation,the exhaust air-fuel ratio is a mixture of air from the cylinderswithout injected fuel, and a lean air fuel ratio from the cylinderscombusting a lean air-fuel mixture. In this way, fuel vapors from valve168 can be burned in group 210 cylinders even during the AIR/LEAN mode.Note that the engine can also operate in any of the 5 various modesdescribed below with regard to FIG. 3A 1, for example. Note that, asdescribed in more detail below, the mode selected may be based ondesired engine output torque, whether idle speed control is active,exhaust temperature, and various other operating conditions.

Referring now to FIG. 2B, a system similar to that in FIG. 2A is shown,however a dual fuel vapor purge system is shown with first and secondpurge valves 168A and 168B. Thus, independent control of fuel vaporsbetween each of groups 210 and 212 is provided. When the system of FIG.2B is operated in an AIR/LEAN mode, first combustion group 210 isoperated at a lean air-fuel ratio (typically leaner than about 18:1),second combustion group 212 is operated without fuel injection, and fuelvapor purging can be enabled to group 210 via valve 168A (and disabledto group 212 via valve 168B). Alternatively, first combustion group 210is operated without fuel injection, second combustion group 212 isoperated at a lean air-fuel ratio, and fuel vapor purging can be enabledto group 212 via valve 168B (and disabled to group 210 via valve 168A).In this way, the system can perform the AIR/LEAN mode in differentcylinder groups depending on operating conditions, or switch between thecylinder groups to provide even wear, etc.

Referring now to FIG. 2C, a V-6 engine is shown with first group 250 onone bank, and second group 252 on a second bank. The remainder of theexhaust system is similar to that described above in FIGS. 2A and 2B.The fuel vapor purge system has a single control valve 168 fed tocylinders in group 250.

When the system of FIG. 2C is operated in an AIR/LEAN mode, firstcombustion group 250 is operated at a lean air-fuel ratio (typicallyleaner than about 18:1) and second combustion group 252 is operatedwithout fuel injection. Thus, in this case, and during this operation,the exhaust air-fuel ratio is a mixture of air from the cylinderswithout injected fuel, and a lean air fuel ratio from the cylinderscombusting a lean air-fuel mixture. In this way, fuel vapors from valve168 can be burned in group 250 cylinders even during the AIR/LEAN mode.Note that the engine can also operate in any of the 5 various modesdescribed below with regard to FIG. 3A 1, for example.

Referring now to FIG. 2D, a system similar to that in FIG. 2C is shown,however a dual fuel vapor purge system is shown with first and secondpurge valves 168A and 168B. Thus, independent control of fuel vaporsbetween each of groups 250 and 252 is provided. When the system of FIG.2D is operated in an AIR/LEAN mode, first combustion group 250 isoperated at a lean air-fuel ratio (typically leaner than about 18:1),second combustion group 252 is operated without fuel injection, and fuelvapor purging can be enabled to group 250 via valve 168A (and disabledto group 212 via valve 168B). Alternatively, first combustion group 250is operated without fuel injection, second combustion group 252 isoperated at a lean air-fuel ratio, and fuel vapor purging can be enabledto group 252 via valve 168B (and disabled to group 250 via valve 168A).In this way, the system can perform the AIR/LEAN mode in differentcylinder groups depending on operating conditions, or switch between thecylinder groups to provide even wear, etc. Note that the engine can alsooperate in any of the 5 various modes described below with regard toFIG. 3A 1, for example.

Referring now to FIG. 2E, a V-6 engine is shown similar to that of FIG.2C, with the addition of an exhaust gas recirculation (EGR) system andvalve 178. As illustrated in FIG. 2E, the EGR system takes exhaustgasses exhausted from cylinders in cylinder group 250 to be fed to theintake manifold (downstream of the throttle). The EGR gasses then passto both cylinder groups 250 and 252 via the intake manifold. Theremainder of the exhaust system is similar to that described above inFIGS. 2A and 2B. Note that, as above, the engine can also operate in anyof the 5 various modes described below with regard to FIG. 3A 1, forexample.

Referring now to FIG. 2F, a system similar to that in FIG. 2E is shown,however a dual fuel vapor purge system is shown with first and secondpurge valves 168A and 168B. Further, EGR gasses are taken from group252, rather than 250. Again, the engine can also operate in any of the 5various modes described below with regard to FIG. 3A 1, for example.

Referring now to FIG. 2G, a system similar to that in FIG. 2A is shown,however an exhaust gas recirculation system and valve 178 is shown forintroducing exhaust gasses that are from some cylinders in group 210 andsome cylinders in group 212 into the intake manifold downstream of thethrottle valve. Again, the engine can also operate in any of the 5various modes described below with regard to FIG. 3A 1, for example.

Referring now to FIG. 2H, a system similar to that in FIG. 2G is shown,however a dual fuel vapor purge system is shown with first and secondpurge valves 168A and 168B. Again, the engine can also operate in any ofthe 5 various modes described below with regard to FIG. 3A 1, forexample.

Referring now to FIG. 2I, a V-6 engine is shown with first cylindergroup 250 on a first bank, and second cylinder group 252 on a secondbank. Further, a first exhaust path is shown coupled to group 250including an upstream emission control device 220 and a downstreamemission control device 226. Further, an exhaust manifold sensor 230, anintermediate sensor 232 between devices 220 and 226, and a downstreamsensor 239 are shown for measuring various exhaust gas air-fuel ratiovalues. In one example, devices 220 and 226 are three way catalystshaving one or more bricks enclosed therein. Similarly, a second exhaustpath is shown coupled to group 252 including an upstream emissioncontrol device 222 and a downstream emission control device 228.Further, an exhaust manifold sensor 234, an intermediate sensor 236between devices 222 and 228, and a downstream sensor 241 are shown formeasuring various exhaust gas air-fuel ratio values. In one example,devices 222 and 228 are three way catalysts having one or more bricksenclosed therein.

Continuing with FIG. 2I, both groups 250 and 252 have a variable valveactuator (270 and 272, respectively) coupled thereto to adjust operationof the cylinder intake and/or exhaust valves. In one example, these arevariable cam timing actuators as described above in FIGS. 1A and 1B.However, alternative actuators can be used, such as variable valve lift,or switching cam systems. Further, individual actuators can be coupledto each cylinder, such as with electronic valve actuator systems.

Note that FIG. 2I, as well as the rest of the figures in FIG. 2 areschematic representations. For example, the purge vapors from valve 168can be delivered via intake ports with inducted air as in FIG. 2J,rather than via individual paths to each cylinder in the group as inFIG. 2I. And as before, the engine can also operate in various enginemodes, such as in FIG. 3A 1, or as in the various routines describedbelow herein.

Referring now to FIG. 2J, a system similar to that of FIG. 2I is shownwith an alternative fuel vapor purge delivery to the intake manifold,which delivery fuel vapors from valve 168. Note that such a system canbe adapted for various systems described in FIG. 2 above and below, asmentioned with regard to FIG. 2I, although one approach may provideadvantages over the other depending on the operating modes of interest.

Referring now to FIG. 2K, a V-8 engine is shown with a first group ofcylinders 210 spanning both cylinder banks, and a second group ofcylinders 212 spanning both cylinder banks. Further, an exhaust systemconfiguration is shown which brings exhaust gasses from the group 212together before entering an emission control device 260. Likewise, thegasses exhausted from device 260 are mixed with untreated exhaust gassesfrom group 210 before entering emission control device 262. This isaccomplished, in this example, via a cross-over type exhaust manifold.Specifically, exhaust manifold 256 is shown coupled to the inner twocylinders of the top bank of group 212; exhaust manifold 257 is showncoupled to the outer two cylinders of the top bank of group 210; exhaustmanifold 258 is shown coupled to the inner two cylinders of the bottombank of group 210; and exhaust manifold 259 is shown coupled to theouter two cylinders of the bottom bank of group 212. Then, manifolds 257and 258 are fed together and then fed to mix with gasses exhausted fromdevice 250 (before entering device 262), and manifolds 256 and 259 arefed together and fed to device 260. Exhaust gas air-fuel sensor 271 islocated upstream of device 260 (after manifolds 256 and 259 join).Exhaust gas air-fuel sensor 273 is located upstream of device 262 beforethe gasses from the group 210 join 212. Exhaust gas air-fuel sensor 274is located upstream of device 262 after the gasses from the group 210join 212. Exhaust gas air-fuel sensor 276 is located downstream ofdevice 276.

In one particular example, devices 260 and 262 are three way catalysts,and when the engine operates in a partial fuel cut operation, group 212carries out combustion oscillating around stoichiometry (treated indevice 260), while group 210 pumps are without injected fuel. In thiscase, device 262 is saturated with oxygen. Alternatively, when bothcylinder groups are combusting, both devices 260 and 262 can operate totreat exhausted emissions with combustion about stoichiometry. In thisway, partial cylinder cut operation can be performed in an odd fire V-8engine with reduced noise and vibration.

Note that there can also be additional emission control devices (notshown), coupled exclusively to group 210 upstream of device 262.

Referring now to FIG. 2L, another V-8 engine is shown with a first groupof cylinders 210 spanning both cylinder banks, and a second group ofcylinders 212 spanning both cylinder banks. However, in this example, afirst emission control device 280 is coupled to two cylinders in the topbank (from group 212) and a second emission control device 282 iscoupled to two cylinders of the bottom bank (from group 212). Downstreamof device 280, manifold 257 joins exhaust gasses from the remaining twocylinders in the top bank (from group 210). Likewise, downstream ofdevice 282, manifold 258 joins exhaust gasses from the remaining twocylinders in the bottom bank (from group 210). Then, these two gasstreams are combined before entering downstream device 284.

In one particular example, devices 280, 282, and 284 are three waycatalysts, and when the engine operates in a partial fuel cut operation,group 212 carries out combustion oscillating around stoichiometry(treated in devices 280 and 282), while group 210 pumps are withoutinjected fuel. In this case, device 284 is saturated with oxygen.Alternatively, when both cylinder groups are combusting, devices 280,282, and 284 can operate to treat exhausted emissions with combustionabout stoichiometry. In this way, partial cylinder cut operation can beperformed in an odd fire V-8 engine with reduced noise and vibration.

Note that both FIGS. 2K and 2L shows a fuel vapor purge system and valve168 for delivering fuel vapors to group 210.

Referring now to FIG. 2M, two banks of a V8 engine are shown. The oddfire V8 engine is operated by, in each bank, running two cylinders aboutstoichiometry and two cylinders with air. The stoichiometric and airexhausts are then directed through a bifurcated exhaust pipe to abifurcated metal substrate catalyst, described in more detail below withregard to FIGS. 14 and 15. The stoichiometric side of the catalystreduces the emissions without the interference from the air side of theexhaust. The heat from the stoichiometric side of the exhaust keeps thewhole catalyst above a light-off temperature during operatingconditions. When the engine is then operated in 8-cylinder mode, the airside of the catalyst is in light-off condition and can reduce theemissions. A rich regeneration of the air side catalyst can also beperformed when changing from 4 to 8 cylinder mode whereby the 2cylinders that were running air would be momentarily operated rich toreduce the oxygen storage material in the catalyst prior to returning tostoichiometric operation, as discussed in more detail below. Thisregeneration can achieve 2 purposes: 1) the catalyst will function in3-way operation when the cylinders are brought back to stoichiometricoperation and 2) the regeneration of the oxygen storage material willresult in the combustion of the excess CO/H2 in the rich exhaust andwill raise the temperature of the catalyst if it has cooled duringperiod when only air was pumped through the deactivated cylinders

Continuing with FIG. 2M, exhaust manifold 302 is shown coupled to theinner two cylinders of the top bank (from group 212). Exhaust manifold304 is shown coupled to the outer two cylinders of the top bank (fromgroup 210). Exhaust manifold 308 is shown coupled to the inner twocylinders of the bottom bank (from group 210). Exhaust manifold 306 isshown coupled to the outer two cylinders of the bottom bank (from group212). Exhaust manifolds 302 and 304 are shown leading to an inlet pipe(305) of device 300. Likewise, exhaust manifolds 306 and 308 are shownleading to an inlet pipe (307) of device 302, which, as indicated above,are described in more detail below. The exhaust gasses from devices 300and 302 are mixed individually and then combined before entering device295. Further, a fuel vapor purge system and control valve 168 are showndelivering fuel vapors to group 212.

Again, as discussed above, an I-4 engine could also be used, where theengine has a similar exhaust and inlet configuration to one bank of theV-8 engine configurations shown above and below in the various Figures.

FIGS. 2N, 2O, and 2P are similar to FIGS. 2K, 2L, and 2M, respectively,except for the addition of a first and second variable valve actuationunits, in this particular example, variable cam timing actuators 270 and272.

Referring now to FIG. 2Q, an example V-6 engine is shown with emissioncontrol devices 222 and 224. In this example, there is no emissioncontrol device coupled exclusively to group 250. A third emissioncontrol device (not shown) can be added downstream. Also, FIG. 2Q showsan example V-6 engine, however, others can be used in thisconfiguration, such as a V-10, V-12, etc.

Referring now to FIG. 2R, an example system is shown where fuel vaporsare passed to all of the cylinders, and in the case of cylinder fuel cutoperation, fuel vapor purging operating is suspended.

Referring now to FIGS. 2S and 2T, still another example system is shownfor an engine with variable valve operation (such as variable cam timingfrom devices 270 and 272), along with a fuel vapor purging system havinga single valve 168 in 2S, and dual purge valves 168A,B in 2T.

There are various fuel vapor modes for FIGS. 2A-2T, some of which arelisted below:

-   -   operate the first group of cylinders lean with fuel vapor purge        (and injected fuel), and the other group inducting gasses        without injected fuel    -   operate the first group of cylinders stoichiometric with fuel        vapor purge (and injected fuel), and the other group inducting        gasses without injected fuel    -   operate the first group of cylinders rich with fuel vapor purge        (and injected fuel), and the other group inducting gasses        without injected fuel    -   operate the first group of cylinders lean with fuel vapor purge        (and injected fuel), and the other group stoichiometric without        fuel vapors    -   operate the first group of cylinders stoichiometric with fuel        vapor purge (and injected fuel), and the other group        stoichiometric without fuel vapors    -   operate the first group of cylinders rich with fuel vapor purge        (and injected fuel), and the other group stoichiometric without        fuel vapors    -   operate the first group of cylinders lean with fuel vapor purge        (and injected fuel), and the other group lean without fuel        vapors    -   operate the first group of cylinders stoichiometric with fuel        vapor purge (and injected fuel), and the other group lean        without fuel vapors    -   operate the first group of cylinders rich with fuel vapor purge        (and injected fuel), and the other group lean without fuel        vapors    -   operate the first group of cylinders lean with fuel vapor purge        (and injected fuel), and the other group rich without fuel        vapors    -   operate the first group of cylinders stoichiometric with fuel        vapor purge (and injected fuel), and the other group rich        without fuel vapors    -   operate the first group of cylinders rich with fuel vapor purge        (and injected fuel), and the other group rich without fuel        vapors    -   operate the first group of cylinders lean with fuel vapor purge        (and injected fuel), and the other group rich with fuel vapors        (and injected fuel)    -   operate the first group of cylinders stoichiometric with fuel        vapor purge (and injected fuel), and the other group rich with        fuel vapors (and injected fuel)    -   operate the first group of cylinders rich with fuel vapor purge        (and injected fuel), and the other group rich with fuel vapors        (and injected fuel)    -   operate the first group of cylinders lean with fuel vapor purge        (and injected fuel), and the other group lean with fuel vapors        (and injected fuel)    -   operate the first group of cylinders stoichiometric with fuel        vapor purge (and injected fuel), and the other group lean with        fuel vapors (and injected fuel)    -   operate the first group of cylinders rich with fuel vapor purge        (and injected fuel), and the other group lean with fuel vapors        (and injected fuel)    -   operate the first group of cylinders lean with fuel vapor purge        (and injected fuel), and the other group stoichiometric with        fuel vapors (and injected fuel)    -   operate the first group of cylinders stoichiometric with fuel        vapor purge (and injected fuel), and the other group        stoichiometric with fuel vapors (and injected fuel)    -   operate the first group of cylinders rich with fuel vapor purge        (and injected fuel), and the other group stoichiometric with        fuel vapors (and injected fuel)

Each of these modes can include further variation, such as different VCTtiming between cylinder banks, etc. Also note that operation at acylinder cut condition provides a practically infinite air-fuel ratio,since substantially no fuel is being injected by the fuel injectors forthat cylinder (although there may be some fuel present due to fuelaround the intake valves and in the intake port that will eventuallydecay away). As such, the effective air-fuel ratio is substantiallygreater than about 100:1, for example. Although, depending on the engineconfiguration, it could vary between 60:1 to practically an infinitevalue.

Regarding the various systems shown in FIGS. 2A-R, different systemconfigurations can present their own challenges that are addressedherein. For example, V-8 engines, such as in FIG. 2A, for example, canhave uneven firing order, so that if it is desired to disable a group of4 cylinders, then two cylinders on each bank are disabled to provideacceptable vibration. However, this presents challenges since, as shownin FIG. 2A, some exhaust system configurations treat emissions from theentire bank together. Further, as shown in FIGS. 2S-2T, a single valveactuator can be used to adjust all of the valves of cylinders in a bank,even though some cylinders in the bank are disabled, while others areoperating. Unlike such V-8 engines, some V-6 engines can be operatedwith a cylinder bank disabled, thus allowing an entire cylinder bank tobe a group of cylinders that are operated without fuel injection. Eachof these different types of systems therefore has its own potentialissues and challenges, as well as advantages, as discussed and addressedby the routines described in more detail below.

Note a bifurcated induction system (along firing order groups) can alsobe used for the fresh air. Such a system would be similar to the systemof FIG. 2T, except that the valves 168A and 168B would be replaced byelectronically controlled throttles. In this way, fuel vapor purge couldbe fed to these two bifurcated induction systems, along with airflow, sothat separate control of fuel vapor purge and airflow could be achievedbetween groups 210 and 212. However, as discussed above with regard toFIGS. 2I and 2J, for example, the VCT actuators can be used to obtaindiffering airflows (or air charges) between the cylinders of groups 250and 252, without requiring a split induction system.

Several control strategies may be used to take advantage of the abilityto provide differing air amounts to differing cylinder groups, asdiscussed in more detail below. As one example, separate control ofairflow to different cylinder groups (e.g., via VCT actuators 270 and272 in FIGS. 2I and 2J), can be used in split ignition operation toallow more (or less) air flow into a group of cylinders. Also, undersome conditions there may be no one air amount that satisfiesrequirements of combustion stability, heat generation, and netpower/torque. For example, the power producing cylinder group may have aminimum spark advance for stability, or the heat producing cylindergroup may have a maximum heat flux due to material constraints. Bank-VCTand/or bifurcated intake could be used to achieve these requirementswith different air amounts selected for different cylinder groups.

Another control strategy example utilizing a bifurcating inlet (or usingVCT in a V6 or V10) would allow lower pumping losses in cylinder cut-outmode by changing the air flow to that group, where VCT is not solelyassociated with a firing group.

Further details of control routines are included below which can be usedwith various engine configurations, such as those described in FIGS.2A-2T. As will be appreciated by one of ordinary skill in the art, thespecific routines described below in the flowcharts may represent one ormore of any number of processing strategies such as event-driven,interrupt-driven, multi-tasking, multi-threading, and the like. As such,various steps or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments of the invention described herein,but is provided for ease of illustration and description. Although notexplicitly illustrated, one of ordinary skill in the art will recognizethat one or more of the illustrated steps or functions may be repeatedlyperformed depending on the particular strategy being used. Further,these figures graphically represent code to be programmed into thecomputer readable storage medium in controller 12.

Referring now to FIG. 3A 1, a graph is shown illustrating engine outputversus engine speed. In this particular description, engine output isindicated by engine torque, but various other parameters could be used,such as, for example: wheel torque, engine power, engine load, orothers. The graph shows the maximum available torque that can beproduced in each of five operating modes. Note that a percentage ofavailable torque, or other suitable parameters, could be used in placeof maximum available torque. Further note that the horizontal line doesnot necessarily correspond to zero engine brake torque. The fiveoperating modes in this embodiment include:

-   -   Operating all cylinders with air pumping through and        substantially no injected fuel (note:

the throttle can be substantially open, or closed, during this mode),illustrated as line 3A1-8 in the example presented in FIG. 3A 1;

-   -   Operating some cylinders lean of stoichiometry and remaining        cylinders with air pumping through and substantially no injected        fuel (note: the throttle can be substantially open during this        mode), illustrated as line 33 ba in the example presented in        FIG. 3A 1;    -   Operating some cylinders at stoichiometry, and the remaining        cylinders pumping air with substantially no injected fuel (note:        the throttle can be substantially open during this mode), shown        as line 3A1-4 in the example presented in FIG. 3A 1;    -   Operating all cylinders lean of stoichiometry (note: the        throttle can be substantially open during this mode, shown as        line 3A1-2 in the example presented in FIG. 3A 1;    -   Operating all cylinders substantially at stoichiometry (or        slightly rich of stoichiometry) for maximum available engine        torque, shown as line 3A1-0 in the example presented in FIG. 3A        1.

Described above is one exemplary embodiment where an 8-cylinder engineis used and the cylinder groups are broken into two equal groups.However, various other configurations can be used, as discussed aboveand below. In particular, engines of various cylinder numbers can beused, and the cylinder groups can be broken down into unequal groups aswell as further broken down to allow for additional operating modes. Forthe example presented in FIG. 3A 1 in which a V-8 engine is used, lines3A1-16 shows operation with 4 cylinders operating with air andsubstantially no fuel, line 3A1-14 shows operation with four cylindersoperating at stoichiometry and four cylinders operating with air, line3A1-12 shows 8 cylinders operating lean, line 3A1-10 shows 8 cylindersoperating at stoichiometry, and line 3A1-18 shows all cylindersoperating without injected fuel.

The above described graph illustrates the range of available torques ineach of the described modes. In particular, for any of the describedmodes, the available engine output torque can be any torque less thanthe maximum amount illustrated by the graph. Also note that in any modewhere the overall mixture air-fuel ratio is lean of stoichiometry, theengine can periodically switch to operating all of the cylindersstoichiometric or rich. This is done to reduce the stored oxidants(e.g., NOx) in the emission control device(s). For example, thistransition can be triggered based on the amount of stored NOx in theemission control device(s), or the amount of NOx exiting the emissioncontrol device(s), or the amount of NOx in the tailpipe per distancetraveled (mile) of the vehicle.

To illustrate operation among these various modes, several examples ofoperation are described. The following are simply exemplary descriptionsof many that can be made, and are not the only modes of operation. As afirst example, consider operation of the engine along trajectory A. Inthis case, the engine initially is operating with all cylinders in thefuel-cut mode. Then, in response to operating conditions, it is desiredto change engine operation along trajectory A. In this case, it isdesired to change engine operation to operating with four cylindersoperating lean of stoichiometry, and four cylinders pumping air withsubstantially no injected fuel. In this case, additional fuel is addedto the combusting cylinders to commence combustion, and correspondinglyincrease engine torque. Likewise, it is possible to follow the reversetrajectory in response to a decrease in engine output.

As a second example, consider the trajectory labeled B. In this example,the engine is operating with all cylinders combusting at substantiallystoichiometry. In response to a decrease in desired engine torque, 8cylinders are operated in a fuel cut condition to provide a negativeengine output torque.

As a third example, consider the trajectory labeled C. In this example,the engine is operating with all cylinders combusting at a lean air-fuelmixture. In response to a decrease in desired engine torque, 8 cylindersare operated in a fuel cut condition to provide a negative engine outputtorque. Following this, it is desired to change engine operation tooperating with four cylinders operating lean of stoichiometry, and fourcylinders pumping air with substantially no injected fuel. Finally, theengine is again transitioned to operating with all cylinders combustingat a lean air-fuel mixture.

As a fourth example, consider the trajectory labeled D. In this example,the engine is operating with all cylinders combusting at a lean air-fuelmixture. In response to a decrease in desired engine torque, 8 cylindersare operated in a fuel cut condition to provide a negative engine outputtorque. Likewise, it is possible to follow the reverse trajectory inresponse to an increase in engine output

Continuing with FIG. 3A 1, and lines 3A1-10 to 3A1-18 in particular, anillustration of the engine output, or torque, operation for each of theexemplary modes is described. For example, at engine speed N1, line3A1-10 shows the available engine output or torque output that isavailable when operating in the 8-cylinder stoichiometric mode. Asanother example, line 3A1-12 indicates the available engine output ortorque output available when operating in the 8-cylinder lean mode atengine speed N2. When operating in the 4-cylinder stoichiometric and4-cylinder air mode, line 3A1-14 shows the available engine output ortorque output available when operating at engine speed N3. Whenoperating in the 4-cylinder lean, 4-cylinder air mode, line 3A1-16indicates the available engine or torque output when operating at enginespeed N4. Finally, when operating in the 8-cylinder air mode, line 3A1-18 indicates the available engine or torque output when operating atengine speed N5.

Referring now to FIG. 3A 2, another graph is shown illustrating engineoutput versus engine speed. The alternative graph shows the maximumavailable torque that can be produced in each of 3 operating modes. Aswith regard to FIG. 3A 1, note that the horizontal line does notnecessarily correspond to zero engine brake torque. The three operatingmodes in this embodiment include:

-   -   Operating all cylinders with air pumping through and        substantially no injected fuel (note: the throttle can be        substantially open, or closed, during this mode), illustrated as        line 3A2-6 in the example presented in FIG. 3A 2;    -   Operating some cylinders at stoichiometry, and the remaining        cylinders pumping air with substantially no injected fuel (note:        the throttle can be substantially open during this mode), shown        as line 3A2-4 in the example presented in FIG. 3A 2;    -   Operating all cylinders substantially at stoichiometry (or        slightly rich of stoichiometry) for maximum available engine        torque, shown as line 3A2-2 in the example presented in FIG. 3A        2.

Referring now to FIG. 3B, a routine for controlling the fuel vehiclepurge is described. In general terms, the routine adjusts valve 168 tocontrol the fuel vapor purging supplied to the cylinder group 210 to becombusted therein. As illustrated in FIG. 2A, the fuel vapor can bepurged to cylinders in group 210 while these cylinders are carrying outstoichiometric, rich, or lean combustion. Furthermore, the cylinders ingroup 212 can be carrying out combustion at stoichiometric, rich, orlean, or operating with air and substantially no injector fuel. In thisway, it is possible to purge fuel vapor while operating in the air-leanmode. Further, it is possible to purge fuel vapors while operating in astoichiometric-air mode.

Referring now specifically to FIG. 3B, in step 310, the routinedetermines whether fuel vapor purging is requested. This determinationcan be based on various parameters, such as whether the engine is in awarmed up state, whether the sensors and actuators are operating withoutdegradation, and/or whether the cylinders in group 210 are operatingunder feedback air-fuel ratio control. When the answer to step 310 isyes, the routine continues to step 312 to activate valve 168. Then, instep 314, the routine estimates the fuel vapor purge amount in the fuelvapors passing through valve 168. Note that there are various ways toestimate fuel vapor purging based on the valve position, engineoperating conditions, exhaust gas air-fuel ratio, fuel injection amountand various other parameters. One example approach is described belowherein with regard to FIG. 4. Next, in step 316, the routine adjusts theopening of valve 168 based on the estimated purge amount to provide adesired purge amount. Again, there are various approaches that can beused to produce this control action such as, for example: feedbackcontrol, feed-forward control, or combinations thereof. Also, thedesired purge amount can be based on various parameters, such as enginespeed and load, and the state of the charcoal canister in the fuel vaporpurging system. Further, the desired purge amount can be based on theamount of purge time completed.

From step 316, the routine continues to step 318 to determine whetherthe estimated purge amount is less than a minimum purge value (min_prg).Another indication of whether fuel vapor purging is substantiallycompleted is whether the purge valve 168 has been fully opened for apredetermined amount of operating duration. When the answer to step 318is no, the routine continues to end. Alternatively, when the answer tostep 318 is yes, the routine continues to step 320 to disable fuel vaporpurging and close valve 168. Also, when the answer to step 310 is no,the routine also continues to step 322 to disable the fuel vaporpurging.

In this way, it is possible to control the fuel vapor purging to asubset of the engine cylinders thereby allowing different operatingmodes between the cylinder groups.

Referring now to FIG. 3C, an example routine for controlling the systemas shown in FIG. 2B is described. In general, the routine controls thefuel vapor purge valves 168 a and 168 b to selectively control fuelvapor purge in cylinder groups 210, or 212, or both. In this way,different sets of cylinders can be allowed to operate in differentoperating modes with fuel vapor purging, thereby providing for moreequalized cylinder operation between the groups.

Referring now specifically to FIG. 3C, in step 322, the routinedetermines whether fuel vapor purging is requested as described abovewith regard to step 310 of FIG. 3B. When the answer to step 322 is yes,the routine continues to step 324 to select the cylinder group, orgroups, for purging along with selecting the purge valve or valves toactuate. The selection of cylinder groups to provide fuel vapor purgingis a function of several engine and/or vehicle operating conditions. Forexample, based on the quantity of fuel vapor purge that needs to beprocessed through the cylinders, the routine can select either onecylinder group or both cylinder groups. In other words, when greaterfuel vapor purging is required, both cylinder groups can be selected.Alternatively, when lower amounts of fuel vapor purging are required,the routine can select one of groups 210 and 212. When it is decided toselect only one of the two cylinder groups due to, for example, low fuelvapor purging requirements, the routine selects from the two groupsbased on various conditions. For example, the decision of which group toselect can be based on providing equal fuel vapor purging operation forthe two groups. Alternatively, the cylinders operating at the more leanair-fuel ratio can be selected to perform the fuel vapor purging toprovide improved combustion stability for the lean operation. Stillother selection criteria could be utilized to select the number andwhich groups to provide fuel vapor purging. Another example is that thewhen only a single cylinder group is selected, the routine alternatesbetween which group is selected to provide more even wear between thegroups. For example, the selection could attempt to provide a consistentnumber of engine cycles between the groups. Alternatively, the selectioncould attempt to provide a consistent amount of operating time betweenthe groups.

When the first group is selected, the routine continues to step 326 toactuate valve 168 a. Alternatively, when the second group is selected,the routine continues to step to actuate valve 168 b in step 328.Finally, when both the first and second groups are selected, the routinecontinues to step 330 to actuate both valves 168 a and 168 b.

From either of steps 326, 328, or 330, the routine continues to step 332to estimate the fuel vapor purging amount. As described above, there arevarious approaches to estimate fuel vapor purge amount, such asdescribed below herein with regard to FIG. 4. Next, in step 334, theroutine continues to adjust the selected purge valve (or valves) basedon the estimated purge amount to provide the desired purge amount. Asdescribed above, there are various approaches to providing feedbackand/or feedforward control to provide the desired purge amount. Further,the desired purge amount can be selected based on various operatingconditions, such as, for example: engine speed and engine load.

Continuing with FIG. 3C, in step 336, the routine determines whether theestimated purge amount is less than the minimum purge amount (min_prg).As discussed above herein with regard to step 318 of FIG. 3B. Asdiscussed above, when the answer to step 336 is yes, the routine ends.Alternatively, when the answer to step 336 is no, the routine alsocontinues to step 338 to disable fuel vapor purging. When the answer tostep 336 is no, the routine continues to the end.

In this way, it is possible to provide both cylinder groups with theability to operate in the air/lean, or air/stoichiometric mode andcombust fuel vapors, or the other group operates with air andsubstantially no injected fuel.

Note also that the routines of FIGS. 3A and 3B could be modified tooperate with the configurations of FIGS. 2C- 2T.

Referring now to FIG. 4, a routine for estimating fuel vapor purgeamounts is described. Note that this example shows calculations for useon a V8 type engine with four cylinders per bank and with two cylinderspurging and two cylinders without purge on a bank as illustrated in FIG.2A, for example. However, the general approach can be expanded to othersystem configurations as is illustrated in detail below. The followingequations describe this example configuration.

The measured air-fuel ratio in the exhaust manifold (λ_(meas)) can berepresented as:λ_(meas)=(0.5 dm _(aprg) /dt+0.5 dm _(air) /dt)/(0.5 dm _(fprg) /dt+dm_(finj1) /dt+dm _(finj2) /dt+dm _(finj3) /dt+dm _(finj4) /dt)where:

dm_(aprg)/dt=is the mass air flow rate in the total fuel vapor purgeflow;

dm_(air)/dt=is the mass air flow rate measured by the mass air flowsensor flowing through the throttle body;

dm_(fprg)/dt=is the fuel flow rate in the total fuel vapor purge flow;

dm_(finj1)/dt=is the fuel injection in the first cylinder of the bankcoupled to the air-fuel sensor measuring λ_(meas);

dm_(finj2)/dt=is the fuel injection in the second cylinder of the bankcoupled to the air-fuel sensor measuring λ_(meas);

dm_(finj3)/dt=is the fuel injection in the third cylinder of the bankcoupled to the air-fuel sensor measuring λ_(meas);

dm_(finj4)/dt=is the fuel injection in the fourth cylinder of the bankcoupled to the air-fuel sensor measuring λ_(meas);

When operating in with two cylinders inducting air with substantially noinjected fuel, and fuel vapors delivered only to two cylinders carryingout combustion in that bank, this reduces to:λ_(meas)=(0.5 dm _(aprg) /dt+0.5 dm _(air) /dt)/(0.5 dm _(fprg) /dt+dm_(finj2) /dt+dm _(finj3) /dt)

Then, using an estimate of dm_(aprg)/dt based on manifold pressure andpurge valve position, the commanded values for dm_(finj2)/dt anddm_(finj3)/dt, the measured air-fuel ratio from the sensor for λ_(meas),and the measure airflow from the mass air flow sensor for dm_(air)/dt,an estimate of dm_(fprg)/dt can be obtained. As such, the concentrationof fuel vapors in the purge flow can then be found as the ratio ofdm_(fprg)/dt to dm_(aprg)/dt. Also, as discussed in more detail below,the fuel injection is adjusted to vary dm_(finj2)/dt and dm_(finj3)/dtto provide a desired air-fuel ratio of the exhaust gas mixture asmeasured by λ_(meas). Finally, in the case where cylinders 1 and 4 arecombusting injected fuel, the commanded injection amounts can be used todetermine the amount of fuel injected so that the first equation can beused to estimate fuel vapors.

In this way, it is possible to estimate the fuel vapor purge contentfrom a sensor seeing combustion from cylinders with and without fuelvapor purging.

Referring now specifically to FIG. 4, first in step 410, the routinecalculates a fresh air amount to the cylinders coupled to themeasurement sensor from the mass air flow sensor and fuel vapor purgingvalve opening degree. Next, in step 412, the routine calculates the fuelflow from the fuel injectors. Then, in step 414, the routine calculatesconcentration of fuel vapors from the air and fuel flows.

Note that if there are two fuel vapor purge valves, each providingvapors to separate cylinder banks and sensor sets, then the abovecalculations can be repeated and the two averaged to provide an averageamount of vapor concentration from the fuel vapor purging system.

Referring now to FIG. 5, a routine is described for controlling amixture air-fuel ratio in an engine exhaust during fuel vapor purging.Specifically, the example routine of FIG. 5 can be used when a sensormeasures exhaust gases that are mixed from cylinders with and withoutfuel vapor purging.

First, in step 510, the routine determines a desired air-fuel ratio(λ_(des)) for the cylinders. Then, in step 512, the routine calculatesan open loop fuel injection amount based on the estimated purge flow andestimated purge concentration to provide an air-fuel mixture in thecylinders with fuel vapor purging at the desired value. Then, in step514, the routine adjusts fuel injection to the cylinders receiving fuelvapor purging to provide the desired mixture air-fuel ratio that ismeasured by the exhaust air-fuel ratio sensor. In this way, theadjustment of the fuel injection based on the sensor feedback can notonly be used to maintain the mixture air-fuel ratio at a desired value,but also as an estimate of fuel vapor purging in the cylinders receivingfuel vapors. Further, the cylinders without fuel vapors can be operatedeither with air and substantially no injected fuel, or at a desiredair-fuel ratio independent of the fuel vapors provided to the othercylinders.

As described above herein, there are various operating modes that thecylinders of engine 10 can experience. In one example, the engine can beoperated with some cylinders combusting stoichiometric or lean gases,with others operating to pump air and substantially no injected fuel.Another operating mode is for all cylinders to be combustingstoichiometric or lean gases. As such, the engine can transition betweenthese operating modes based on the current and other engine operatingconditions. As described below, under some conditions when transitioningfrom less than all the cylinders combusting to all the cylinderscombusting, various procedures can be used to provide a smoothtransition with improved engine operation and using as little fuel aspossible.

As illustrated in the graphs of FIGS. 6A-D, one specific approach totransition from four cylinder operation to eight cylinder operation isillustrated. Note that the particular example of four cylinder to eightcylinder operation could be adjusted based on the number of cylinders inthe engine such as, for example: from three cylinders to six cylinders,from five cylinders to ten cylinders, etc. Specifically, FIG. 6A showstotal engine air flow, FIG. 6B shows the fuel charge per cylinder, FIG.6C shows ignition (spark) angle, and FIG. 6D shows the air-fuel ratio ofcombusting cylinders.

As shown in FIGS. 6A-D, before time T1, four cylinders are initiallycombusting a lean air-fuel ratio and providing a desired engine outputtorque. Then, as engine airflow is decreased, the air-fuel ratioapproaches the stoichiometric value and the engine is operating withfour cylinders combusting a stoichiometric air-fuel ratio and pumpingair with substantially no injected fuel. Then, at time T1, the enginetransitions to eight cylinders combusting. At this time, the desire isto operate all engine cylinders as lean as possible to minimize thetorque increase by doubling the number of combusting cylinders. However,since the engine typically has a lean combustion air-fuel ratio limit(as indicated by the dashed dot line in FIG. 6D), it is not possible tocompensate all the increased torque by combusting a lean air-fuel ratioin all the cylinders. As such, not only is the fuel charge per cylinderdecreased, but the ignition angle is also decreased until the airflowcan be reduced to the point at which all the cylinders can be operatedat the lean limit.

In other words, from time T1 to T2, engine torque is maintained bydecreasing engine airflow and retarding ignition timing until the enginecan be operated with all the cylinders at the air-fuel ratio limit toprovide the same engine output as was provided before the transitionfrom four cylinders to eight cylinders. In this way, it is possible toprovide a smooth transition, while improving fuel economy by using leancombustion in the enabled cylinders, as well as the previouslystoichiometric combusting cylinders and thus reducing the amount ofignition timing retard after the transition that is required.

This improved operation can be compared to the case where the transitionis from four cylinders to eight cylinders, with the eight cylinderscombusting at stoichiometry. In this case, which is illustrated by thedashed lines in FIGS. 6A-6D, a greater amount of ignition timing retardfor a longer duration, is required to maintain engine torquesubstantially constant during the transition. As such, since thisrequires more ignition timing retard, over a longer duration, more fuelis wasted to produce engine output than with the approach of the solidlines in FIGS. 6A-6D, one example of which is described in the routineof FIG. 7.

Referring now to FIG. 7, a routine is described for controlling atransition from less than all the cylinders combusting to all thecylinders combusting, such as the example from four cylinders to eightcylinders illustrated in FIGS. 6A-D.

First, in step 710, the routine determines whether a transition has beenrequested to enable the cylinders operating to pump air andsubstantially no injected fuel. When the answer to step 710 is yes, theroutine continues to step 712 to determine whether the system iscurrently operating in the air-lean mode. When the answer to step 712 isyes, the routine transitions the engine to the air-stoichiometric modeby decreasing engine airflow. Next, from step 714, or when the answer tostep 712 is no, the routine continues to step 716. In step 716, theroutine calculates a lean air-fuel ratio with all cylinders operating(λ_(f)) at the present airflow to provide the current engine torque. Inthe example of transitioning from four cylinders to eight cylinders,this air-fuel ratio is approximately 0.5 if the current operatingconditions are in the air-stoichiometric mode. In other words, all thecylinders would require half the fuel to produce the same torque as halfthe cylinders at the current amount of fuel.

Next, in step 718, the routine calculates the lean limit air-fuel ratio(λ_(LL)) for the conditions after the transition. In other words, theroutine determines the combustion stability lean limit which isavailable after the transition for the operating conditions present.Then, in step 720, the routine determines whether the calculated leanair-fuel ratio to maintain engine torque (λ_(f)) is greater than thelean limit air-fuel ratio. If the answer to step 720 is no, thetransition is enabled without ignition timing retard. In this case, theroutine transitions the cylinders to the new air-fuel ration calculatedin step 716 to maintain engine torque.

However, the more common condition is that the required air-fuel ratioto maintain engine torque is greater than the lean limit for theoperating conditions. In this case, the routine continues to step 722 totransition the air-fuel ratio at the lean air-fuel limit and compensatethe torque difference via the ignition timing retard. Further, theairflow is reduced until the engine can operate at the lean air-fuelratio limit (or within a margin of the limit) without ignition timingretard.

In this way, the transition to enabling cylinders with lean combustioncan be utilized to improve fuel economy and maintain engine torqueduring the transition. Thus, not only is the torque balanced over thelong term, but also over the short term using air-fuel enleanment inaddition to ignition timing retard, if necessary. Further, thistransition method achieves the a synergistic effect of rapid catalystheating since the ignition timing retard and enleanment help increaseheat to the exhaust system to rapidly heat any emission control devicescoupled to deactivated cylinders. Note that various modifications can bemade to this transition routine. For example, if transitioning to enablepurging of NOx stored in the exhaust system, rich operation can followthe enleanment once airflow has been reduced.

Referring now to FIG. 8, a routine is described for controlling enginecylinder valve operation (intake and/or exhaust valve timing and/orlift, including variable cam timing, for example) depending on engineconditions and engine operating modes. In general terms, the routine ofFIG. 8 allows engine cylinder valve operation for different groups ofcylinders during engine starting to help compensate for variations inignition timing between the groups.

First, in step 810, the routine determines whether the presentconditions represent an engine starting condition. This can bedetermined by monitoring if the engine is being turned by a startingmotor. Note however, that engine starting can include not only theinitial cranking by the starter, but also part of the initial warm upphase from a cold engine condition. This can be based on variousparameters, such as engine speed, time since engine start, or others.Thus, when the answer to step 810 is yes, the routine then determineswhether the engine is already in a warmed up condition in step 812. Thiscan be based on, for example, engine coolant temperature.

When the answer to step 812 is no, the routine sets the flag (flag_LS)to one. Otherwise, the flag is set to zero at 816. Next, the routinecontinues to step 818 where a determination is made as to whether splitignition operation is requested. One example of split ignition operationincludes the following method for rapid heating of the emission controldevice when an emission control device(s) is below a desired operatingtemperature. Specifically, in this approach, the ignition timing betweentwo cylinders (or two or more cylinder groups) is set differently. Inone example, the ignition timing for the first group (spk_grp_(—)1) isset equal to a maximum torque, or best, timing (MBT_spk), or to anamount of ignition retard that still provides good combustion forpowering and controlling the engine. Further, the ignition timing forthe second group (spk_grp_(—)2) is set equal to a significantly retardedvalue, for example −29°. Note that various other values can be used inplace of the 29° value depending on engine configuration, engineoperating conditions, and various other factors. Also, the power heatflag (ph_enable) is set to zero.

The amount of ignition timing retard for the second group (spk_grp_(—)2)used can vary based on engine operating parameters, such as air-fuelratio, engine load, and engine coolant temperature, or catalysttemperature (i.e., as catalyst temperature rises, less retard in thefirst and/or second groups, may be desired). Further, the stabilitylimit value can also be a function of these parameters.

Also note, as described above, that the first cylinder group ignitiontiming does not necessarily have to be set to maximum torque ignitiontiming. Rather, it can be set to a less retarded value than the secondcylinder group, if such conditions provide acceptable engine torquecontrol and acceptable vibration. That is, it can be set to thecombustion stability spark limit (e.g., −10 degrees). In this way, thecylinders on the first group operate at a higher load than theyotherwise would if all of the cylinders were producing equal engineoutput. In other words, to maintain a certain engine output (forexample, engine speed, engine torque, etc.) with some cylindersproducing more engine output than others, the cylinders operating at thehigher engine output produce more engine output than they otherwisewould if all cylinders were producing substantially equal engine output.

An advantage to the above aspect is that more heat can be created byoperating some of the cylinders at a higher engine load withsignificantly more ignition timing retard than if operating all of thecylinders at substantially the same ignition timing retard. Further, byselecting the cylinder groups that operate at the higher load, and thelower load, it is possible to minimize engine vibration. Thus, the aboveroutine starts the engine by firing cylinders from both cylinder groups.Then, the ignition timing of the cylinder groups is adjusted differentlyto provide rapid heating, while at the same time providing goodcombustion and control.

Also note that the above operation provides heat to both the first andsecond cylinder groups since the cylinder group operating at a higherload has more heat flux to the catalyst, while the cylinder groupoperating with more retard operates at a high temperature.

Note that in such operation, the cylinders have a substantiallystoichiometric mixture of air and fuel. However, a slightly lean mixturefor all cylinders, or part of the cylinders, can be used.

Also note that all of the cylinders in the first cylinder group do notnecessarily operate at exactly the same ignition timing. Rather, therecan be small variations (for example, several degrees) to account forcylinder to cylinder variability. This is also true for all of thecylinders in the second cylinder group. Further, in general, there canbe more than two cylinder groups, and the cylinder groups can have onlyone cylinder.

Further note that, as described above, during operation according to oneexample embodiment, the engine cylinder air-fuel ratios can be set atdifferent levels. In one particular example, all the cylinders can beoperated substantially at stoichiometry. In another example, all thecylinders can be operated slightly lean of stoichiometry. In stillanother example, the cylinders with more ignition timing retard areoperated slightly lean of stoichiometry, and the cylinders with lessignition timing retard are operated slightly rich of stoichiometry.Further, in this example, the overall mixture of air-fuel ratio is setto be slightly lean of stoichiometry. In other words, the lean cylinderswith the greater ignition timing retard are set lean enough such thatthere is more excess oxygen than excess rich gasses of the rich cylindergroups operating with less ignition timing retard.

Continuing with FIG. 8, when the answer to step 818 is yes, the routineenables the split ignition operations in step 820 by setting the flag(PH_ENABLE_Flg) to one.

Then, in step 822, the desired valve operation (in this case valvetiming) for the first and second group of cylinders is calculatedseparately and respectively based on the conditions of the cylindergroups, including the air flow, air/fuel ratio, engine speed, enginetorque (requested and actual), and ignition timing. In this way, anappropriate amount of air charge and residual charge can be provided tothe different cylinder groups to better optimize the conditions for therespective ignition timing values used in the cylinders.

The desired variable cam timings for the cylinder groups can also bebased on various other parameters, such as catalyst temperature(s)and/or whether flag_CS is set to zero or one. When operating in thesplit ignition operation, at least during some conditions, this resultsin different VCT settings between different cylinder groups to provideimproved engine operation and catalyst heating. In this way, the airflow to the cylinder with more advanced ignition timing can be used tocontrol engine output torque, as well as the torque imbalance betweenthe cylinder groups. Further, the airflow to the cylinder with moreretarded ignition timing can be used to control the combustionstability, or heat flux produced. Also, if the engine is not equippedwith VCT, but rather variable valve lift, or electrically actuatedvalves, then different airflow can be provided to different cylindersvia valve lift, or variation of timing and/or lift of the electricallyactuated valves. Furthermore, if the engine is equipped with multiplethrottle valves (e.g., one per bank), then airflow to each group can beadjusted via the throttle valve, rather than via variations in VCT.

Continuing with FIG. 8, when the answer to step 818 is no, the routinecontinues to step 824 where a determination is made as to whether fuelinjector cut-out operation of a cylinder, or cylinder groups, isenabled. When the answer to step 824 is yes, the routine continues tostep 826 to calculate the desired cam timing (s) for operating cylindergroup(s) taking into account the cylinder cut-out operation. In otherwords, different valve timings can be selected, at least during someconditions, based on whether cylinder cut-out operation is engaged.Thus, the VCT timing for the respective cylinder groups is based on theair-fuel ratio of combustion in the group combusting air and injectedfuel, while the VCT timing for the group without fuel injection isselected to, in one example, minimize engine pumping losses.Alternatively, when transitioning into, or out of, the partial or totalcylinder cut-out operation, the VCT timing for the respective cylindergroups is adjusted based on this transition. For example, when enablingcombustion of cylinder previous in cylinder cut-out operation, the VCTtiming is adjusted to enable efficient and low emission re-starting ofcombustion, which can be a different optimal timing for the cylinderswhich were already carrying out combustion of air and injected fuel.This is described in more detail below with regard to FIG. 12, forexample.

Alternatively, when the answer to step 824 is no, the valve timing forthe cylinder groups is selected based on engine speed and load, forexample.

In this way, it is possible to select appropriate valve timing toimprove cylinder cut-out operation. When firing groups coincide with VCT(or bifurcated intake groups), it is possible to optimize the amount ofcatalyst heating (or efficient engine operation) depending on thevehicle tolerance to different types of excitation (NVH) given theoperating conditions.

Specifically, in one example, NVH performance can be improved byreducing the airflow to cylinders with significantly retarded ignitiontiming to reduce any effect of combustion instability that may occur.Likewise, in another example, engine torque output can be increased,without exacerbating combustion instability, by increasing airflow tothe cylinder(s) with more advanced ignition timing. This can beespecially useful during idle speed control performed via an idle bypassvalve, or via the electronic throttle, where even though total airflowis being increased, that increased airflow can be appropriatelyallocated to one cylinder group or another depending on the ignitiontiming split used.

Note that an alternative starting routine is described in FIG. 34.

Referring now to FIG. 9, a routine is described for identifying pedaltip-out conditions, and using such information to enable or disable fuelinjection to cylinders, or cylinder groups, of the engine. First, instep 910, the routine identifies whether a tip-out condition has beendetected. Note that there are various approaches to detecting a tip-outcondition, such as, for example: detecting if whether the pedal has beenreleased by the vehicle driver's foot, whether a requested engine outputhas decreased below a threshold value (for example, below zero valueengine brake torque), whether a requested wheel torque has decreasedbelow a threshold level, or various others. When the answer to step 910is yes and a tip-out condition has been detected, the routine continuesto step 912. In step 912, the routine determines whether the requestedengine output is less than threshold T1. In one example, this thresholdis the minimum negative engine output that can be achieved with all thecylinders combusting. This limit can be set due to various enginecombustion phenomena, such as engine misfires, or significantlyincreased emissions. Also note that various types of requested engineoutput can be used, such as, for example: engine torque, engine braketorque, wheel torque, transmission output torque, or various others.When the answer to step 912 is yes, the routine continues to step 914.In step 914, the routine enables a fuel cut operation, which isdiscussed in more detail below with regard to FIG. 10. Alternatively,when the answer to either step 910 or 912 is no, the routine continuesto step 916 in which combustion in all the cylinders of the engine iscontinued.

Note that the fuel cut operation enabled in step 914 can be varioustypes of cylinder fuel cut operation. For example, only a portion of theengine's cylinders can be operated in the fuel cut operation, or a groupof cylinders can be operated in the fuel cut operation, or all of theengine cylinders can be operated in the fuel cut operation. Furthermore,the threshold T1 discussed above with regard to step 912 can be avariable value that is adjusted based on the current engine conditions,including engine load and temperature.

Referring now to FIG. 10, an example routine is described forcontrolling fuel cut operation, which can be used with a variety ofsystem configurations, such as, for example, FIGS. 2A-2H. First, in step1010, the routine determines whether fuel cut operation has been enabledas discussed above with regard to step 914 of FIG. 9. When the answer tostep 1010 is yes, the routine continues to step 1012. In step 1012, theroutine determines the number of cylinder groups to disable based on therequested engine output and current engine and vehicle operatingconditions. These operating conditions include the catalyst operatingconditions, temperature (engine temperature and/or catalyst temperature)and engine speed. Next, in step 1014, the routine determines the numberof cylinders in the groups to be disabled based on the requested engineoutput and engine and vehicle operating conditions. In other words, theroutine first determines the number of cylinder groups to be disabled,and then determines within those groups, the number of cylinders of thegroups to be disabled. These determinations are also selected dependingon the engine and exhaust catalyst configuration. For example, in casesusing a downstream lean NOx trap, in addition to disabling cylinders,the remaining active cylinders can be operated at a lean air-fuel ratio.

Continuing with FIG. 10, in step 1016, the routine determines whetherthe requested engine output is greater than a threshold T2, such as whena vehicle driver tips-in to the vehicle pedal. When the answer to step1016 is no, the routine continues to step 1018 to determine whethertemperature of the emission control devices coupled to disabledcylinders is less than a minimum temperature (min_temp). As such, theroutine monitors the requested engine output and the temperature of theemission control devices to determine whether to re-enable cylindercombustion in the activated cylinders. Thus, when the answer to eitherstep 1016 or 1018 is yes, the routine continues to step 1020 to disablefuel cut operation and enable combustion. This enabling can enable allthe cylinders to return to combustion or only a part of the activatedcylinders to return to combustion. Whether all or only a portion of thecylinders are reactivated depends on various engine operating conditionsand on the exhaust catalyst configuration. For example, when three-waycatalysts are used without a lean NOx trap, all of the cylinders may beenabled to carry out combustion. Alternatively, when a downstream leanNOx trap is used, all or only a portion of the cylinders may bere-enabled at a lean air-fuel ratio, or some of the cylinders can bere-enabled to carry out stoichiometric combustion.

Note that before the fuel cut operation is enabled, the engine can beoperating with all the cylinders carrying out lean, stoichiometric, orrich engine operation.

Referring now to FIG. 11, a routine is described for performing idlespeed control of the engine, taking into account fuel vapor purging.First, in step 1110, the routine determines whether idle speed controlconditions are present. Idle speed conditions can be detected bymonitoring whether the pedal position is lower than a preselectedthreshold (indicating the driver's foot is off the pedal) and the enginespeed is below a threshold speed (for example 1000 RPM). When the answerto step 1110 is yes, the routine continues to step 1112. In step 1112,the routine determines whether lean combustion is enabled based on thecurrent engine operating conditions, such as exhaust temperature, enginecoolant temperature, and other conditions, such as whether the vehicleis equipped with a NOx trap. When the answer to step 1112 is no, theroutine continues to step 1114.

In step 1114, the routine maintains the desired idle speed via theadjustment of air flow to the engine. In this way, the air flow isadjusted so that the actual speed of the engine approaches the desiredidle speed. Note that the desired idle speed can vary depending onoperating conditions such as engine temperature. Next, in step 1116, theroutine determines whether fuel vapors are present in the engine system.In one example, the routine determines whether the purge valve isactuated. When the answer to step 1116 is yes, the routine continues tostep 1118. In step 1118, the routine adjusts the fuel injection amount(to the cylinders receiving fuel vapors) to maintain the desiredair-fuel ratio, as well as compensate for the fuel vapors, while fuelinjected to cylinders combusting without fuel vapors (if any) can be setto only a feed-forward estimate, or further adjusted based on feedbackfrom the exhaust gas oxygen sensor. Thus, both cylinders with andwithout fuel vapor are operated at a desired air-fuel ratio by injectingless fuel to the cylinders with fuel vapors. In one example, the desiredcombustion air-fuel ratio oscillates about the stoichiometric air-fuelratio, with feedback from exhaust gas oxygen sensors from the engine'sexhaust. In this way, the fuel injection amount in the cylinders withfuel vapors is compensated, while the fuel injection amount to cylindersoperating without fuel vapors is not affected by this adjustment, andall of the cylinders combusting are operated about stoichiometry.

Next, in step 1120, the routine determines whether the fuel injectionpulse width (to the cylinders with fuel vapors) is less than a minimumvalue (min_pw). When the answer to step 1120 is yes, the routinecontinues to step 1122 to disable fuel vapor purging and close the purgevalve (s). In this way, the routine prevents the fuel injection pulsewidth from becoming lower than a minimum allowed pulse width to operatethe injectors.

When the answer to either step 1116, or 1120 is no, the routinecontinues to the end.

When the answer to step 1112 is yes, the routine continues to step 1124.Then, in step 1124, the routine maintains the desired idle speed viaadjustment of fuel injection. In this way, the fuel injection amount isadjusted, so that the actual speed of the engine approaches the desiredidle speed. Note that this lean combustion conditions includesconditions where some cylinders operate with a lean air-fuel ratio, andother cylinders operate without injected fuel. Next, in step 1126, theroutine determines whether fuel vapors are present in the engine(similar to that in step 1116). When the answer is yes, the routinecontinues to step 1128 where air flow is adjusted to maintain theair-fuel ratio in the combusting cylinders and compensate for the fuelvapors. Note that there are various ways to adjust the air flow to thecylinders carrying out combustion, such as by adjusting the throttleposition of the electronically controlled throttle plate. Alternatively,air flow can be adjusted by changing valve timing and/or lift, such asby adjusting a variable cam timing actuator.

Next, in step 1130, a routine determines whether the cylinder air-fuelratio (of cylinders carrying out combustion) is less than a minimumvalue (afr_min). In one example, this is a minimum lean air-fuel ratio,such as 18:1. In addition, the routine monitors whether air flow is atthe maximum available air flow for the current engine operatingconditions. If not, the engine first attempts to increase air flow byfurther opening the throttle, or adjusting valve timing and/or lift.However, when air flow is already at a maximum available amount, theroutine continues to step 1132 to disable lean combustion. The routinemay still allow continued cylinder fuel cut-out operation since thisoperation provides for maximum fuel vapor purging in a stoichiometriccondition as will be discussed below.

When the answer to either step 1110, 1126, or 1130, is no, the routinecontinues to the end.

In this way, it is possible to operate with fuel vapor purging andimprove operation of both lean and stoichiometric combustion.Specifically, by using fuel injection to maintain idle speed during leanconditions, and air flow to maintain idle speed during non-leanconditions, it is possible to provide accurate engine idle speed controlduring both conditions. Also, by disabling lean operation, yetcontinuing to allow cylinder fuel cut-out operation, when the fuelvapors are too great to allow lean combustion, it is possible to improvethe quantity of fuel vapor purge that can be processed. In other words,during cylinder fuel cut-out operation, all the fuel vapors are fed to aportion of the cylinders, for example as shown in FIG. 2C. However,since less than all the cylinders are carrying out the combustion togenerate engine output, these cylinders operate at a higher load, andtherefore a higher total requirement of fuel to be burned. As such, theengine is less likely to experience conditions where the fuel injectorsare less than the minimum pulse width than compared if all the cylinderswere carrying out combustion with fuel vapors. In this way, improvedfuel vapor purging capacity can be achieved.

Referring now to FIGS. 12A and 12B, routines are described forcontrolling cylinder valve adjustment depending, in part, on whethersome or all of the cylinders are operating an a fuel-cut state. Ingeneral, the routine adjusts the cylinder valve timing, and/or valvelift, based on this information to provide improved operation. Also, theroutine of FIG. 12A is an example routine that can be used for systemconfigurations such as those shown in FIGS. 2N, 2O, 2P, 2S and/or 2T.The routine of FIG. 12B is an example routine that can be used forsystem configurations such as those shown in FIGS. 2I and 2J.

First, in step 1210, the routine determines whether the engine isoperating in a full or partial fuel injector cut-out operation. When theanswer to step 1210 is yes, the routine continues to step 1212. In step1212, the routine determines a desired cylinder valve actuation amountfor a first and second actuator. In this particular example, where afirst and second variable cam timing actuator are used to adjust camtiming of cylinder intake and/or exhaust valves, the routine calculatesa desired cam timing for the first and second actuator (VCT_DES1 andVCT_DES2). These desired cam timing values are determined based on thecylinder cut-out condition, as well as engine operating conditions suchas the respective air-fuel ratios and ignition timing values betweendifferent cylinder groups, throttle position, engine temperature, and/orrequested engine torque. In one embodiment, the operating conditionsdepend on operating mode. Specifically, in addition to engine speedversus torque, the following conditions are considered in an idle speedmode: engine speed, closed pedal, crank start, engine temperature, andair charge temperature. In addition to engine speed versus torque, thefollowing conditions are considered in a part throttle or wide openthrottle condition: rpm, desired brake torque, and desired percenttorque.

In one example, where the routine is applied to a system such as in FIG.2S or 2T, the routine can further set a cam timing per bank of theengine, where the cylinder groups have some cylinders from each bank inthe group. Thus, a common cam timing is used for both cylinders with andwithout combustion from injected fuel. As such, the desired cam timingmust not only provide good combustion in the cylinders carrying outcombustion, but also maintain a desired manifold pressure by adjustingairflow though the engine, along with the throttle. Note that in manyconditions, this results in a different cam timing for the combustingcylinders than would be obtained if all of the cylinders were carryingout combustion in the cylinder group.

Alternatively, when the answer to step 1210 is no, the routine continuesto step 1214 to calculate the desired valve actuator settings (VCT_DES1and VCT_DES2) based on engine conditions, such as engine speed,requested engine torque, engine temperature, air-fuel ratio, and/orignition timing.

From either of steps 1212 or 1214, the routine continues to step 1216where a determination is made as to whether the engine is transitioninginto, or out of, full or partial fuel injector cut-out operation. Whenthe answer to step 1216 is no, the routine continues to step 1218 whereno adjustments are made to the determined desired cylinder valve values.

Otherwise, when the answer to step 1216 is yes, the routine continues tostep 1220 where the routine determines whether the transition is tore-enable fuel injection, or cut fuel injection operation. When it isdetermined that a cylinder, or group of cylinders, is to be re-enabled,the routine continues to step 1222. Otherwise, the routine continues tothe end.

In step 1222, the routine adjusts the desired cam timing values(VCT_DES1 and/or VCT_DES2) of cylinder valves coupled to cylinders beingre-enabled to a re-starting position (determine based on engine coolanttemperature, airflow, requested torque, and/or duration of fuel-cutoperation). In this way, it is possible to have improved re-starting ofthe cylinders that were in fuel-cut operation. In the case where bothcylinders are operated in a fuel cut operation, all of the cylinders canbe restarted at a selected cam timing that provides for improvedstarting operation.

Note that due to different system configurations, this may also adjustcam timing of cylinders already carrying out combustion. As such,additional compensation via throttle position or ignition timing can beused to compensate for increases or decreases engine output due to theadjustment of cam timing before the transition. The details of thetransition are discussed in more detail above and below, such asregarding FIG. 6, for example.

Referring now to FIG. 12B, an alternative embodiment for controllingcylinder valve actuation based on fuel-cut operation is described.First, in step 1230, the routine determines whether the engine isoperating in a full or partial fuel injector cut-out operation. When theanswer to step 1230 is yes, the routine continues to step 1232. In step1232, the routine determines a desired cylinder valve actuation amountfor an actuator coupled to a group of cylinders in which fuel injectionis disabled. In one example, this is a desired cam timing value.Further, the routine also calculates an adjustment to throttle position,along with the cam timing, to adjust the engine output to provide arequested engine output. In one example, the requested engine output isa negative (braking) engine torque value. Further, in step 1232, theroutine adjusts the cam timing for the combusting cylinders (if any)based on conditions in those combusting cylinders.

Alternatively, the routine can set the desired cylinder valve actuationamount for deactivated cylinders to provide a desired engine pumpingloss amount, since adjusting the cam timing of the cylinders will varythe intake manifold pressure (and airflow), thus affecting enginepumping losses. Note that in some cases, this results in a different camtiming being applied to the group of cylinders combusting than the groupof cylinders in fuel-cut operation.

Alternatively, when the answer to step 1230 is no, the routine continuesto step 1234 to calculate the desired valve actuator settings (VCT_DES1and VCT_DES2) based on engine conditions, such as engine speed,requested engine torque, engine temperature, air-fuel ratio, and/orignition timing as shown in step 1214.

From either of steps 1232 or 1234, the routine continues to step 1236where a determination is made as to whether the engine is transitioninginto, or out of, full or partial fuel injector cut-out operation. Whenthe answer to step 1236 is no, the routine continues to step 1238 whereno adjustments are made to the determined desired cylinder valve values.

Otherwise, when the answer to step 1236 is yes, the routine continues tostep 1240 where the routine determines whether the transition is tore-enable fuel injection, or cut fuel injection operation. When it isdetermined that a cylinder, or group of cylinders, is to be re-enabled,the routine continues to step 1242. Otherwise, the routine continues tothe end.

In step 1242, the routine adjusts the cam timing actuators coupled todisabled cylinders to a re-starting position. Note that the cylinderscan re-start at a lean air-fuel ratio, a rich air-fuel ratio, or atstoichiometry (or to oscillate about stoichiometry). In this way, bymoving the cam timing that provides for improved starting, whileoptionally leaving the cam timing of cylinders already combusting at itscurrent condition, it is possible provide improved starting operation.

Referring now to FIGS. 13A and 13B, routines and corresponding exampleresults are described for controlling partial and full cylinder cutoperation to reestablish the oxygen storage amount in the downstreamthree-way catalyst, as well as to reestablish the fuel puddle in theintake manifold to improve transient fuel control. Note that theroutines FIGS. 13A and 13C can be carried out with various systemconfigurations as represented in FIG. 2. For example, the routine ofFIG. 13A can be utilized with the system of FIG. 2Q, for example.Likewise, the routine of FIG. 13C can be utilized with the system ofFIG. 2R. Referring now specifically to FIG. 13A, in step 1302, theroutine determines whether partial cylinder fuel cut-out operation ispresent. When the answer to step 1302 is yes, the routine continues tostep 1304. In step 1304, the routine determines whether the cylinderscarrying out combustion are operating about stoichiometry. When theanswer to step 1304 is yes, the routine continues to step 1306. In step1306, the routine determines whether transition to operate both cylindergroups to combust an air-fuel ratio that oscillates about stoichiometryhas been requested by the engine control system. When the answer to anyof steps 1302, 1304, or 1306 are no, the routine continues to the end.

When the answer to step 1306 is yes, the routine continues to step 1308.In step 1308, the routine enables fuel injection in the disabledcylinder group at a selected rich air-fuel ratio, while continuingoperation of the other cylinder carrying out combustion aboutstoichiometry. The selected rich air-fuel ratio for the re-enabledcylinders is selected based on engine operating conditions such as, forexample: catalyst temperature, engine speed, catalyst space velocity,engine load, and such or requested engine torque. From step 1308, theroutine continues to step 1310, where a determination is made as towhether the estimated actual amount of oxygen stored in the downstreamthree-way catalyst (O2_d_act) is greater than a desired amount of oxygen(O2_d_des). When the answer to step 1310 is yes, the routine continuesto step 1312 to continue the rich operation of the re-enabled cylindergroup at a selected rich air-fuel ratio, and the oscillation aboutstoichiometry of the air-fuel ratio of the already combusting cylinders.As discussed above with regard to step 1308, the rich air-fuel ratio isselected based on engine operating conditions, and various dependingupon them. From step 1312, the routine returns to step 1310 to againmonitor the amount of oxygen stored in the downstream three-waycatalyst. Alternatively, the routine of FIG. 13A can also monitor aquantity of fuel in the puddle in the intake manifold of the cylindersthat are being re-enabled in step 1310.

When the answer to step 1310 is no, the routine continues to step 1314which indicates that the downstream three-way catalyst has beenreestablished at a desired amount of stored oxygen between the maximumand minimum amounts of oxygen storage, and/or that the fuel puddle inthe intake manifold of the various enabled cylinders has beenreestablished. As such, in step 1314, the routine operates both groupsabout stoichiometry. In this way, it is possible to re-enable thecylinders from a partial cylinder cut-out operation and reestablish theemission control system to a situation in which improved emissioncontrol can be achieved.

The operation of FIG. 13A is now illustrated via an example as shown inFIGS. 13B1 and 13B2. FIG. 13B 1 shows the air-fuel ratio of group 1,while FIG. 13B 2 shows the air-fuel ratio of group 2. At time T0, bothcylinder groups operate to carry out combustion about the stoichiometricvalue. Then, at time T1, it is requested to transition the engine topartial cylinder cut operation, and therefore the cylinder group 1 isoperating at a fuel cut condition. As shown in FIG. 13B 1, the air-fuelratio is infinitely lean and designated via the dashed line that is at asubstantially lean air-fuel ratio. Then, at time T2, it is desired tore-enable the partially disabled cylinder operation, and therefore thecylinder group 1 is operated at a rich air-fuel ratio as shown in FIG.13B 1, this rich air-fuel ratio varies as engine operating conditionschange. The rich operation of group 1 and the stoichiometric operationof group 2 continues until time T3, at which point it is determined thatthe downstream emission control device has been reestablished to anappropriate amount of oxygen storage. As described elsewhere herein, theidentification of when to discontinue the rich regeneration operationcan be based on estimates of stored oxygen, and/or based on when asensor downstream of the downstream emission control device switches. Attime T3, both cylinder groups are returned to stoichiometric operation,as shown in FIGS. 13B1 and 13B2.

As such, improved engine operation is achieved since the second cylindergroup can remain combusting at stoichiometry throughout thesetransitions, yet the downstream emission control device can have itsoxygen storage reestablished via the rich operation of the firstcylinder group. This reduces the amount of transitions in the secondcylinder group, thereby further improving exhaust emission control.

Referring now to FIG. 13C, a routine is described for controllingcylinder cut-out operation where both cylinder groups are disabled.First, in step 1320, the routine determines whether all cylinders arepresently in the cylinder cut operation. When the answer to step 1320 isyes, the routine continues to step 1322 to determine whether thecylinders will be carrying out stoichiometric combustion when enabled.When the answer to step 1322 is yes, the routine continues to step 1324to determine whether the transition of one or two groups is requested tobe enabled. In other words, the routine determines whether it has beenrequested to enable only one cylinder group, or to enable two cylindergroups to return to combustion. When the answer to step 1324, or step1322, or step 1320, is no, the routine ends.

Alternatively, when in step 1324, it is requested to enable bothcylinder groups, the routine continues to step 1326. In step 1326, theroutine operates fuel injection in both cylinder groups at a selectedrich air-fuel ratio. Note that the groups can be operated at the samerich air-fuel ratio, or different rich air-fuel ratios. Likewise, theindividual cylinders in the groups can be operated at different richair-fuel ratios. Still further, in an alternative embodiment, only someof the cylinders are operated rich, with the remaining cylindersoperating about stoichiometry.

From step 1326, the routine continues to step 1328. In step 1328, theroutine determines whether the estimated amount of oxygen stored in theupstream three-way catalyst coupled to the first group (O2_u1_act) isgreater than a desired amount of stored oxygen for that catalyst(O2_u1_des). When the answer to step 1320 is no, indicating that theoxygen storage amount has not yet been reestablished in that device, theroutine continues to step 1330 to calculate whether the estimated actualamount of oxygen stored in the emission upstream three-way catalystcoupled to the second group (O2_u2_act) is greater than its desiredamount of stored oxygen (O2_u2_des). When the answer to step 1330 is no,indicating that neither upstream three-way catalyst coupled to therespective first and second groups' cylinders has been reestablished totheir respective desired amounts of stored oxygen, the routine continuesto step 1326, where rich operation in both cylinder groups is continuedat the selected air-fuel ratio. Also note that the selected richair-fuel ratio is adjusted based on engine operating conditions asdescribed above herein with regard to step 1308, for example.

When the answer to step 1328 is yes, indicating that the upstreamthree-way catalyst coupled to the first cylinder group has had itsoxygen amount reestablished, the routine continues to step 1332 totransition the first group to operate about stoichiometry. Next, theroutine continues to step 1334 where it continues operation of thesecond at the selected rich air-fuel ratio and the second group tocombust an air-fuel mixture that oscillates about stoichiometry. Then,the routine continues to step 1336, where a determination is made as towhether the estimated amount of stored oxygen in a downstream three-waycatalyst (which is coupled to at least one of the upstream three-waycatalysts, if not both) is greater than its desired amount of storedoxygen. When the answer to step 1336 is no, the routine returns to step1334 to continue the rich operation in the second group, and thestoichiometric operation in the first group. Alternatively, when theanswer to step 1336 is yes, the routine continues to step 1338 totransition both cylinder groups to operate about stoichiometry.

Continuing with FIG. 13C, when the answer to step 1330 is yes,indicating that the oxygen amount has been reestablished in the emissionupstream three-way catalyst coupled to the second group, the routinetransitions the second group to stoichiometry in step 1342. Then, instep 1344, the routine continues to operate the first cylinder group atthe rich air-fuel ratio and the second cylinder group aboutstoichiometry. Then, the routine continues to step 1346 to again monitorthe oxygen storage amount in the downstream three-way catalyst. Fromstep 1346, when the downstream fuel catalyst has not yet had enoughoxygen depleted to reestablish the oxygen amount, the routine returns tostep 1344. Alternatively, when the answer to step 1346 is yes, theroutine also transitions to step 1338 to have both cylinder groupsoperating about stoichiometry.

From step 1324, when it is desired to transition only one cylinder groupto return to combustion, the routine continues to step 1350 to enablefuel injection in one cylinder group at the selected rich air-fuel ratioand continue fuel cut operation in the other cylinder group. Thisoperation is continued in step 1352. Note that for this illustration, itis assumed that in this case the first cylinder group has been enabledto carry out combustion, while the second cylinder group has continuedoperating at fuel cut operation. However, which cylinder group isselected to be enabled can vary depending on engine operatingconditions, and can be alternated to provide more even cylinder ware.

From step 1352, the routine continues to step 1354, where adetermination is made as to whether the estimated actual amount ofstored oxygen in the upstream three-way catalyst coupled to the firstcylinder group (O2_u1_act) is greater than the desired amount(O2_u1_des). When the answer to step 1354 is no, the routine returns tostep 1352. Alternatively, when the answer to step 1354 is yes, theroutine continues to step 1356 to operate a first cylinder group aboutstoichiometry and continue the operation of the second cylinder group inthe fuel cut operation. Finally, in step 1358, the routine transfers toFIG. 13A to monitor further requests to enable the second cylindergroup.

In this way, it is possible to allow for improved re-enablement ofcylinder fuel cut operation to properly establish the oxygen storage notonly in the upstream three-way catalyst, but also in the downstreamthree-way catalyst without operating more cylinders rich than isnecessary. As described above, this can be accomplished using anestimate of stored oxygen in an exhaust emission control device.However, alternatively, or in addition, it is also possible to useinformation from a centrally mounted air-fuel ratio sensor. For example,a sensor that is mounted at a location along the length of the emissioncontrol device, such as before the last brick in the canister, can beused. In still another approach, downstream sensor(s) can be used todetermine when regeneration of the oxygen storage is sufficientlycompleted.

Example operation of FIG. 13C is illustrated in the graphs of FIGS. 13D1and 13D2. Like FIGS. 13B1 and B2, FIG. 13D 1 shows the air-fuel ratio ofthe first cylinder group and FIG. 13D 2 shows the air-fuel ratio of thesecond cylinder group. At time T0, both cylinder groups are operating tocarry out combustion about the stoichiometric air-fuel ratio. Then, attime T1, it is requested to disable fuel injection in both cylindergroups. As such, both cylinder groups are shown to operate at asubstantially infinite lean air-fuel ratio until time T2. At time T2, itis requested to enable combustion in both cylinder groups. As such, bothcylinder groups are shown operating at a rich air-fuel ratio. Asillustrated in the figures, the level richness of this air-fuel ratiocan vary depending on operating conditions. From times T2 to T3, theoxygen saturated upstream first and second three-way catalysts arehaving the excess oxygen reduced to establish a desired amount of storedoxygen in both the catalysts. At time T3, the upstream three-waycatalyst coupled to the second group has reached the desired amount ofstored oxygen and therefore the second cylinder is transitioned tooperate about stoichiometry. However, since the downstream three-waycatalyst has not yet had its excess oxygen reduced, the first cylindergroup continues at a rich air-fuel ratio to reduce all the stored oxygenin the upstream three-way catalyst coupled to the first group, andtherefore provide reductants to reduce some of the stored oxygen in thedownstream three-way catalyst. Thus, at time T4, the rich operation ofthe first cylinder group has ended since the downstream three-waycatalyst has reached its desired amount of stored oxygen. However, atthis point, since the upstream three-way catalyst is saturated atsubstantially no oxygen storage, the first cylinder groups operateslightly lean for a short duration until T5 to reestablish the storedoxygen in the upstream three-way catalyst. At time T5, then bothcylinder groups operate about stoichiometry until time T6, at which timeagain is desired to operate both cylinders without fuel injection. Thisoperation continues to time T7 at which point it is desired to re-enableonly one of the cylinder groups to carry out combustion. Thus, the firstcylinder group is operated at a rich air-fuel ratio for a short durationuntil the oxygen storage has been reestablished in the first upstreamthree-way catalyst coupled to the first cylinder group. Then, the firstcylinder group returns to stoichiometric operation until time T8. Attime T8, it is desired to re-enable the second cylinder group. At thistime, the second cylinder group operates at a rich air-fuel ratio thatvaries depending on the engine operating conditions to reestablish thestored oxygen in the downstream three-way catalyst. Then, at time T9,the second cylinder group operates slightly lean for a short duration toreestablish some stored oxygen in the upstream three-way catalystcoupled to the second group. Then, both cylinder groups are operated tooscillate above stoichiometry.

In this way, improved operation into and out of cylinder fuel cutconditions can be achieved.

Note that regarding the approach taken in FIG. 13—by re-enabling withrich combustion, any NOx generated during the re-enablement can bereacted in the three way catalyst with the rich exhaust gas, furtherimproving emission control.

Referring now to FIGS. 14 and 15, example emission controls device aredescribed which can be used as devices 300 and/or 302 from FIG. 2. Asdiscussed above, fuel economy improvements can be realized on engines(for example, large displacement engines) by disabling cylinders underconditions such as, for example, low load, or low torque requestconditions. Cylinder deactivation can take place by either deactivatingvalves so the cylinders do not intake or exhaust air or by deactivatingfuel injectors to the inactive cylinders pumping air. In the latterscheme, the bifurcated catalyst described in FIGS. 14 and 15 has theadvantage that they can keep the exhaust from the firing cylindersseparate from the non-firing cylinders so that the emission controldevice (such as, for example, a 3-way catalyst) can effectively convertthe emissions from the firing cylinders. This is true even when used onan uneven firing V8 engine (where disabling cylinders to still give atorque pulse every 180 crank angle degrees requires disabling half ofthe cylinders on one bank and half of the cylinders on the other bank).The bifurcated catalyst approach thus avoids the need to pipe the aircylinders to one catalyst and the firing cylinders to another catalystwith a long pipe to cross the flow from one side of the engine to theother. As such, it is possible, if desired, to maintain current catalystpackage space without requiring complicated crossover piping.

Specifically, FIG. 14 shows a bifurcated catalyst substrate 1410 with afront face 1420 and a rear face (not shown). The substrate is dividedinto an upper portion 1422 and a lower portion 1424. The substrate isgenerally oval in cross-sectional shape; however, other shapes can beused, such as circular. Further, the substrate is formed with aplurality of flow paths formed from a grid in the substrate. In oneparticular example, the substrate is comprised of metal, which helpsheat conduction from one portion of the device to the other, therebyimproving the ability to operate one group of cylinders in a fuel-cutstate. However, a ceramic substrate can also be used.

The substrate is constructed with one or more washcoats applied havingcatalytic components, such as ceria, platinum, palladium, rhodium,and/or other materials, such as precious metals (e.g., metals fromGroup-8 of the periodic table). However, in one example, a differentwashcoat composition can be used on the upper portion of the substrateand the lower portion of the substrate, to accommodate the differentoperating conditions that may be experienced between the two portions.In other words, as discussed above, one or the other of the upper andlower portions can be coupled to cylinders that are pumping air withoutinjected fuel, at least during some conditions. Further, one portion orthe other may be heated from gasses in the other portion, such as duringthe above described cylinder fuel-cut operation. As such, the optimalcatalyst washcoat for the two portions may be different.

In this example, the two portions are symmetrical. This may allow forthe situation where either group of cylinders coupled to the respectiveportions can be deactivated if desired. However, in an alternativeembodiment, the portions can be asymmetrical in terms of volume, size,length, washcoats, or density.

Referring now to FIG. 15, an emission control device 1510 is shownhousing substrate 1410. The device is shown in this example with aninlet cone 1512 an inlet pipe 1514, an exit cone 1516, and an exit pipe1618. The inlet pipe and inlet cone are split into two sides (shown hereas a top and bottom portion; however, any orientation can be used) eachvia dividing plates 1520 and 1522. The two sides may be adjacent, asshown in the figure, but neither portion encloses the other portion, inthis example. The dividing plates keep a first and second exhaust gasflow stream (1530 and 1532) separated up to the point when the exhaustgas streams reach the substrate portions 1422 and 1424, respectively.The dividing plates are located so that a surface of the plate islocated parallel to the direction of flow, and perpendicular to a faceof the substrate 1410. Further, as discussed above, because the pathsthrough the substrate are separated from one another, the two exhaustgas streams stay separated through substrate 1410. Also, exit cone 1516can also have a dividing plate, so that the exhaust streams are mixedafter entering exit pipe 1518.

Continuing with FIG. 15, four exhaust gas oxygen sensors are illustrated(1540, 1542, 1544, and 1546), however only a subset of these sensors canbe used, if desired. As shown by FIG. 15, sensor 1540 measures theoxygen concentration, which can be used to determine an indication ofair-fuel ratio, of exhaust stream 1530 before it is treated by substrate1410. Sensor 1542 measures the oxygen concentration of exhaust stream1532 before it is treated by substrate 1410. Sensor 1544 measures theoxygen concentration of exhaust stream 1530 after it is treated bysubstrate 1410, but before it mixes with stream 1532. Likewise, sensor1546 measures the oxygen concentration of exhaust stream 1532 after itis treated by substrate 1410, but before it mixes with stream 1530.Additional downstream sensors can also be used to measure the mixtureoxygen concentration of streams 1530 and 1532, which can be formed inpipe 1518.

FIG. 15 also shows cut-away views of the device showing an ovalcross-section of the catalyst substrate, as well as the inlet and outletcones and pipes. However, circular cross-sectional pipe, as well assubstrate, can also be used.

Referring now to FIG. 16, a routine is described for selecting a desiredidle speed control set-point for idle speed control which takes intoaccount whether cylinders are deactivated, or whether split ignitiontiming is utilized. Specifically, as shown in step 1610, the routinedetermines a desired idle speed set-point, used for feedback control ofidle speed via fuel and/or airflow adjustment, based on the exhausttemperature, time since engine start, and/or the cylinder cut state.This allows for improved NVH control, and specifically provides, atleast under some conditions, a different idle speed set-point dependingon cylinder cut-operation to better consider vehicle resonances. Thecontrol strategy of desired idle rpm may also be manipulated to improvethe tolerance to an excitation type. For example, in split ignitionmode, a higher rpm set-point may reduce NVH by moving the excitationfrequency away from that which the vehicle is receptive. Thus, the splitignition idle rpm may be higher than that of a non-split ignition mode.

Referring now to FIG. 17, a routine is described for coordinatingcylinder deactivation with diagnostics. Specifically, cylinderdeactivation is enabled and/or affected by a determination of whetherengine misfires have been identified in any of the engine cylinders.

For example, in the case of a V-6 engine as shown in FIG. 2F, if it isdetermined that an ignition coil has degraded in one of the cylinders ingroup 250, then this information can be utilized in enabling, andselecting, cylinder deactivation. Specifically, if the control routinealternatively selects between group 250 and 252 to be deactivated, thenthe routine could modify this selection based on the determination ofdegradation of a cylinder in group 250 to select cylinder deactivationof group 250 repeatedly. In other words, rather than having the abilityto deactivate ether group 250 or group 252, the routine could deactivatethe group which has a cylinder identified as being degraded (and thuspotentially permanently deactivated until repair). In this way, theroutine could eliminate, at least under some conditions, the option ofdeactivating group 252. Otherwise, if group 252 were selected to bedeactivated, then potentially four out of six cylinders would bedeactivated, and reduced engine output may be experienced by the vehicleoperator.

Likewise, if diagnostics indicate that at least one cylinder from eachof groups 250 and 252 should be disabled due to potential misfires, thecylinder cut-out operation is disabled, and all cylinders (except thosedisabled due to potential misfires) are operated to carry outcombustion.

Thus, if the control system has the capability to operate on less thanall the engine's cylinders and still produce driver demanded torque in asmooth fashion, then such a mode may be used to disable misfiringcylinders with minimal impact to the driver. This decision logic mayalso include the analysis of whether an injector cutout pattern wouldresult in all the required cylinders being disabled due to misfire.

FIG. 17 describes an example routine for carryout out this operation.Specifically, in step 1710, the routine determines whether the enginediagnostics have identified a cylinder or cylinders to have potentialmisfire. In one example, when the diagnostic routines identify cylinderor cylinders to have a potential misfire condition, such as due todegraded ignition coils, those identified cylinders are disabled andfuel to those cylinders is deactivated until serviced by a technician.This reduces potential unburned fuel with excess oxygen in the exhaustthat can generate excessive heat in the exhaust system and degradeemission control devices and/or other exhaust gas sensors.

When the answer to step 1710 is no, the routine ends. Alternatively,when the answer to step 1710 is yes, the routine continues to step 1712,where a determination is made as to whether there is a cylinder cutoutpattern for improved fuel economy that also satisfies the diagnosticrequirement that a certain cylinder, or cylinders, be disabled. In otherwords, in one example, the routine determines whether there is acylinder cutout mode that can be used for fuel economy in which all ofthe remaining active cylinders are able to be operated with fuel and aircombusting. When the answer to step 1712 is yes, the routine continuesto step 1714 in which the patterns that meet the above criteria areavailable for injector cutout operation. Patterns of cylinder cutout inwhich cylinders that were selected to remain active have been identifiedto have potential misfire, are disabled.

In this way, it is possible to modify the selection and enablement ofcylinder cutout operation to improve fuel economy, while still allowingproper deactivation of cylinders due to potential engine misfires.

As described in detail above, various fuel deactivation strategies aredescribed in which some, or all, of the cylinders are operated in afuel-cut state depending on a variety of conditions. In one example, allor part of the cylinders can be operated in a fuel-cut state to provideimproved vehicle deceleration and fuel economy since it is possible toprovide engine braking beyond closed throttle operation. In other words,for improved vehicle deceleration and improved fuel economy, it may bedesirable to turn the fuel to some or all of the engine cylinders engineoff under appropriate conditions.

However, one issue that may be encountered is whether the engine speedmay drop too much after the fuel is disabled due to the drop in enginetorque. Depending on the state of accessories on the engine, the stateof the torque converter, the state of the transmission, and otherfactors discussed below, the fuel-off torque can vary.

In one example, an approach can be used in which a threshold enginespeed can be used so that in worst case conditions, the resulting enginespeed is greater than a minimum allowed engine speed. However, in analternative embodiment, if desired, a method can be used thatcalculates, or predicts, the engine speed after turning off the fuel fora vehicle in the present operating conditions, and then uses thatpredicted speed to determine whether the resulting engine speed will beacceptable (e.g., above a minimum allowed speed for those conditions).For example, the method can include the information of whether thetorque converter is locked, or unlocked. When unlocked, a model of thetorque converter characteristics may be used in such predictions.Further, the method may use a minimum allowed engine speed to determinea minimum engine torque that will result from fuel shut off operation toenable/disable fuel shut off. Examples of such control logic aredescribed further below with regard to FIG. 18. Such a method could alsobe used to screen other control system decisions that will affectproduction of engine torque in deceleration conditions, such as whetherto enable/disable lean operation in cylinders that remain combustingwhen others are operated without fuel injection. Examples of suchcontrol logic are described further below with regard to FIG. 19.

Furthermore, such an approach can be useful during tip-out conditions instill other situations, other than utilizing full or partial cylinderfuel deactivation, and other than enabling/disabling alternative controlmodes. Specifically, it can also be used to adjust a requested enginetorque during deceleration conditions in which other types oftransitions may occur, such as transmission gear shifts. This isdescribed in further detail below with regard to FIGS. 20-21.

Referring now to FIG. 18, a model based screening (via a torqueconverter model, for example) for whether to enable (full or partial)fuel shut off operation to avoid excessive engine speed drop isdescribed. First, in step 1810, the routine determines whether thetorque converter is in the locked or partially locked condition. Thepartially locked condition can be encountered when the lock up clutch isbeing applied across the torque converter, yet has not fully coupled thetorque converter input and output. In one example, the determination ofstep 1810 is based upon whether the slip ratio between the input torqueconverter speed and the output torque converter speed is approximatelyone. When the answer to step 1810 is yes, the routine continues to step1822, as discussed in further detail below. When the answer to step 1810is no, the routine continues to step 1812. In step 1812, the routinecalculates the minimum allowed engine speed during a decelerationcondition. In one example, deceleration condition is indicated by adriver tipout of the accelerator pedal (i.e., an accelerator pedalposition less than a threshold value). The minimum allowed engine speedcalculated in step 1812 can be based on a variety of operatingconditions, or selected to be a single value. When the minimum allowedengine speed is dependent upon operating conditions, it can becalculated based on conditions such as, for example: vehicle speed,engine temperature, and exhaust gas temperature.

Continuing with FIG. 18, in step 1814, the routine predicts a turbinespeed at a future interval using vehicle deceleration rate. Thisprediction can be preformed utilizing a simple first order rate ofchange model where the current turbine speed, and current rate ofchange, are used to project a turbine speed at a future instant based ona differential in time. Next, in step 1816, the routine calculates aminimum engine torque required to achieve the calculated minimum allowedengine speed with the predicted turbine speed. Specifically, the routineuses a model of the torque converter to calculate the minimum amount ofengine torque that would be necessary to maintain the engine speed atthe minimum allowed speed taking into account the predicted turbinespeed. The details of this calculation are described below with regardto FIG. 20.

Next, in step 1818, the routine calculates the maximum engine braketorque available to be produced in a potential new control mode that isbeing considered to be used. For example, if the potential new controlmode utilizes cylinder cut operation, this calculation takes intoaccount that some or all of the cylinders may not be producing positiveengine torque. Alternatively, if the new control mode includes leanoperation, then again the routine calculates the maximum engine braketorque available taking into account the minimum available lean air fuelratio.

Make a note that regarding step 1818, the first example is described inmore detail below with regard to FIG. 19.

Next, in step 1820, the routine determines whether the calculatedmaximum engine brake torque in the potential new control mode is greaterthan the engine torque required to achieve, or maintain, the minimumallowed engine speed. If the answer to step 1820 is yes, the routinecontinues to step 1822 to enable the new control mode based on thisengine speed criteria. Alternatively, when the answer to step 1820 isno, the routine continues to step 1824 to disable the transition to thenew control mode based on this engine speed criteria. In this way, it ispossible to enable or disable alternative control modes taking intoaccount their effect on maintaining a minimum acceptable engine speedduring the deceleration condition, and thereby reduce engine stalls.Make a note before the description of step 1810 that the routine to FIG.18 may be preformed during tipout deceleration conditions.

Referring now to FIG. 19, the routine of FIG. 18 has been modified tospecifically apply to the cylinder fuel cut operating scenario. Steps1910-1916 are similar to those described in steps 1810-1816.

From step 1916, the routine continues to step 1918 where the routinecalculates the engine brake torque that will result from turning offfuel at the minimum engine speed. Specifically, the routine calculatesthe engine brake torque that will be produced after turning fuelinjection off to part or all of the cylinders. Further, this calculationof brake torque is preformed at the minimum engine speed. Then, in stop1920, the routine determines whether this resulting engine torque at theminimum engine speed during fuel cut operation is greater then theengine torque required to achieve, or maintain, the minimum allowedengine speed. If so, then the engine torque is sufficient in the fuelcut operation, and therefore the fuel cut operation is enabled based onthis engine speed criteria in step 1922. Alternatively, when the answerto step 1920 is no, then the engine torque that can be produced in thefull or partial fuel cut operation at the minimum engine speed isinsufficient to maintain the minimum engine speed, and therefore thefuel shut-off mode is disable based on this engine speed criteria. Inthis way, it is possible to selectively enable/disable full and/orpartial fuel deactivation to the cylinders in a way that maintainsengine speed at a minimum allowed engine speed. In this way, enginestalls can be reduced.

Note that in this way, at least under some conditions, it is possible toenable (or continue to perform) fuel deactivation to at least onecylinder at a lower engine speed when the torque converter is lockedthan when the torque converter is unlocked. Thus, fuel economy can beimproved under some conditions, without increasing occurrence of enginestalls.

Referring now to FIGS. 20 and 21, a routine is described for clipping adesired engine torque request to maintain engine speed at or above aminimum allowed engine speed during vehicle tip-out conditions utilizingtorque converter characteristics. In this way, it is possible to reducedips in engine speed that may reduce customer feel.

For example, in calibrating a requested impeller torque as a function ofvehicle speed for one or more of the engine braking modes, it isdesirable to select torque values that give good engine braking feel andare robust in the variety of operating conditions. However, this can bedifficult since a variety of factors affect engine braking, and suchvariations can affect the resulting engine speed. Specifically, it canbe desirable to produce less than the required torque to idle underdeceleration conditions to provide a desired deceleration trajectory.However, at the same time, engine speed should be maintained above aminimum allowed engine speed to reduce stall. In other words, one way toimprove the system efficiency (and reduce run-on feel) underdeceleration conditions is to produce less engine torque than needed toidle the engine. Yet at the same time, engine speed drops should bereduced that let engine speed fall below a minimum allowed value.

In one example, for vehicles with torque converters, a model of the opentorque converter can be used to determine the engine torque that wouldcorrespond to a given engine speed (target speed or limit speed), andthus used to allow lower engine torques during deceleration, yetmaintain engine speed above a minimum value. In this case, if there is aminimum allowed engine speed during deceleration, the controller cancalculate the engine torque required to achieve at least that minimumengine speed based on turbine speed. The routine below uses two2-dimensional functions (fn_conv_cpc and fn_conv_tr) to approximate theK-factor and torque ratio across the torque converter as a function ofspeed ratio. This approximation includes coasting operation where theturbine is driving the impeller. In an alternative approach, moreadvanced approximations can be used to provide increased accuracy, ifnecessary.

Note that it is known to use a model of the open torque converter todetermine the engine torque that would correspond to a given enginespeed in shift scheduling for preventing powertrain hunting. I.e., it isknown to forecast the engine speed (and torque converter output speed)after a shift to determine whether the engine can produce enough torqueto maintain tractive effort after an upshift (or downshift) in thefuture conditions. Thus, during normal driving, it is known to screenshift requests to reduce or prevent less than equal horsepower shifts(including a reserve requirement factor), except for accelerations.Further, it is known to include cases where the torque converter islocked, and to include calculations of maximum available engine torque.

Referring now to FIG. 20, a routine is described for calculating theengine brake torque required to spin the engine at a specified enginespeed and turbine speed. First, in step 2010, temporary parameters areinitialized. Specifically, the following 32-bit variables are set tozero: tq_imp_ft_lbf_tmp (temporary value of impeller torque in lbf),tq_imp_Nm_tmp (temporary value of impeller torque in Nm), cpc_tmp(temporary value of K-factor), and tr_tmp (temporary value of torqueratio). Further, the temporary value of the speed ratio(speed_ratio_tmp)=is calculated as a ratio of the temporary turbinespeed (nt_tmp) and the temporary engine speed (ne_tmp), clipped to 1 toreduce noise in the signals.

Then, in step 2012, the routine calculates the temporary K-factor(cpc_tmp) as a function of the speed ratio and converter characteristicsstored in memory using a look-up function, for example. Then, in step2014, a determination is made as to whether the speed ratio (e.g.,speed_ratio_tmp >1.0?). If so, this signifies that the vehicle iscoasting, and positive engine torque is not being transmitted throughthe torque converter. When the answer to step 2014 is Yes, the routinecontinues to step 2016. In step 2016, the routine uses a K-factorequation that uses turbine speed and torque as inputs. Specifically, theimpeller torque is calculated from the following equations:tq _(—) imp _(—) ft _(—) lbf _(—) tmp=nt _(—) tmp*nt _(—) tmp/max((cpc_(—) tmp*cpc _(—) tmp), 10000.0);tr _(—) tmp=f(speed_ratio_(—) tmp);tq _(—) imp _(—) ft _(—) lbf _(—) tmp=−tq _(—) imp _(—) ft _(—) lbf _(—)tmp/tr _(—) tmp;

where the function f stores data about the torque converter to generatethe torque ratio (tr) based on the speed ratio.

Otherwise, when the answer to step 2014 is No, then the K-factorequation uses engine speed and torque as inputs, and the routinecontinues to step 2018. In step 2018, the impeller torque is calculatedfrom the following equations:tq _(—) imp _(—) ft _(—) lbf_tmp=ne_(—) tmp*ne _(—) tmp/max((cpc _(—)tmp*cpc _(—) tmp), 10000.0);

Then, these can be converted to NM units, and losses included, via thefollowing equation in step 2020.tq _(—) imp _(—) Nm _(—) tmp=tq _(—) imp _(—) ft _(—) lbf _(—)tmp*1.3558+tq _(—) los _(—) pmp;

In this way, it is possible to calculate a required torque(tq_imp_Nm_tmp) to maintain engine speed as desired. Example operationis illustrated in FIG. 21. Specifically, FIG. 21 demonstrates theperformance of this torque request clipping/screening during vehicletesting. At approximately 105.5 seconds the accelerator pedal isreleased and the torque based deceleration state machine enters holdsmall positive mode (where a small positive torque is maintained on thedrivetrain) followed by an open loop braking mode, where negative enginetorque is provided in an open-loop fashion. Soon after the tip-out, thetransmission controls command a 3-4 up-shift which will lower theturbine speed below the minimum engine speed target of ˜850 rpm in thisexample, placing a torque load on the engine. This transmission up-shiftmay result in more engine torque being required to hold 850 rpm enginespeed and tqe_decel_req_min (the lower clip applied to thetqe_decel_req_value) therefore jumps to 42 Nm to reflect the highertorque request. The value of tqe_decel_req_min is calculated based onthe torque converter model described above. By keeping the decelerationtorque request from dropping too low, the engine speed behaves asdesired.

Referring now to FIGS. 22-27, a method for managing the cycle averagedtorque during transitions between different cylinder cut-out modes isdescribed. Specifically, such an approach may provide improved torquecontrol during these transitions. Before describing the control routinein detail, the following description and graphs illustrate an examplesituation in which it is possible to better control cycle averagedtorque during the transition (note that this is just one examplesituation in which the method can be used). These graphs use the exampleof an eight cylinder engine where the cylinders on the engine arenumbered in firing order. When the system transitions from firing 1, 3,5, 7 to 2, 4, 6, 8, for example, two cylinders may fire in succession.If the torque produced by all the cylinders during the transition issubstantially the same, the cycle-average torque produced during thetransition may be higher than desired, even though no one cylinderproduces substantially more or less torque, and over a cycle, the samenumber of cylinders is still being fired. In other words, there is asingle, effective shift of half of the cylinders firing earlier in theoverall engine cycle. This torque disturbance may also result in anengine speed disturbance if occurring during idle speed controlconditions. The following figures illustrate an example of this torquedisturbance.

Note that the following description illustrates a simplified example,and is not meant to define operation of the system.

FIG. 22 shows the crankshaft torque for an 8 cylinder engine with allcylinders firing, where the crankshaft torque resulting from the sum ofthe power strokes on the engine are modeled as simple sine waves. Forthe example where four cylinders are operated to produce the same nettorque as all 8 in FIG. 22, then the torque production of each cylinderwould double as shown in FIG. 23.

If this same level of torque was produced by the firing cylinders in 4cylinder mode but the system transitioned from firing 1-3-5-7 to 2-4-6-8with the last cylinder fired before the transition being 3 and the firstcylinder fired after the transition being 4, then crankshaft torquewould be as illustrated in FIG. 24. As shown in FIG. 24, the summing ofthe torques from cylinders 3 and 4 may produce a torque increase duringthis transition point and an increase in the average torque over anengine cycle. The increase could be as much as 12.5% for an 8 cylinderengine, or 16.7% for a 6 cylinder engine due to this overlapping torqueaddition effect. By recognizing this behavior, the control system can beredesigned to reduce the torque produced by the off-going cylinder (3 inthis example) and the on-coming cylinder (4 in this example) such thatthe average torque over a cycle is not increased during a transition.

For an 8 cylinder engine, if the torque produced by cylinders 3 and 4were reduced by approximately 25% each, then the torque profile wouldresemble FIG. 25, with the cycle average torque approximately matchingthe steady 4 or 8 cylinder operation.

In this way, it is possible to improve torque control when transitioningbetween operating in a first mode with the first group combustinginducted air and injected fuel and the second group operating withinducted air and substantially no injected fuel, and operation in asecond mode with the second group combusting inducted air and injectedfuel and the first group operating with inducted air and substantiallyno injected fuel. As indicated in the example, above, before thetransition, engine torque of a last to be combusted cylinder in thefirst group is reduced compared with a previously combusted cylinder inthat group. Further, after the transition, engine torque of a first tobe combusted cylinder in the second group is reduced compared with anext combusted cylinder in that group.

The reduction of one or both of the cylinder can be accomplished in avariety of ways, such as, for example: ignition timing retard, orenleanment of the combusted air and fuel mixture. Further, usingelectric valve actuation, variable valve lift, an electronic throttlevalve, etc., the reduction could be performed by reducing air charge inthe cylinders.

In an alternative embodiment, it may be possible to provide improvetorque control during the transition by reducing torque of only one ofthe last to be fired cylinder in the first group and the first to befired cylinder in the second group. Further, it may be possible toprovide improve torque control during the transition by providingunequal torque reduction in both the last to be fired cylinder in thefirst group and the first to be fired cylinder in the second group.

For example, the torque reduction for the last cylinder of the oldfiring order (in the example discussed above, cylinder 3) and the firstcylinder of the new firing order (cylinder 4) could be implemented inany way such that the total indicated torque produced by these twocylinders was reduced by approximately 25%. For example, if the torquereduction of the last cylinder in the firing order is X*50% and thereduction of the first cylinder in the new firing order is (1−X)*50%,average torque could be maintained. For the example reduction of 25%each, X=0.5.

If all the torque were reduced on the last old firing order cylinder(X=1), the results would be similar to those shown in FIG. 26.Alternatively, if all the torque reduction was accomplished with thefirst cylinder of the new firing order (X=0), then the results would besimilar to those shown in FIG. 27. These are just two example, and Xcould be selected anywhere between 0 and 1.

Referring now to FIGS. 28-33, an approach to reduce engine NVH duringmode transitions between full cylinder operation and partial cylinderoperation (between full cylinder operation and split ignition timingoperation).

FIG. 28 shows the frequency content of the engine at 600 RPM with allcylinders firing at stoichiometry and optimal ignition timing. Thefigure shows a dominant peak at firing frequency of all cylinders firing(FF). This can be compared with FIG. 29, which shows the frequencycontent of the engine at 600 RPM operating in cylinder cut out mode(e.g., fuel to one bank of a V-6 deactivated, or fuel to two cylinderson each bank of a V-8 deactivated), or operating with split ignitiontiming between groups of cylinders. This shows a dominant peak at ½ FF,and a smaller peak at firing frequency due to compression of allcylinders, since deactivated cylinders still pump air. And both FIGS. 28and 29 can be compared with FIG. 30, which shows the frequency contentof the engine at 600 RPM with all cylinders firing at a lean air-fuelratio and/or with regarded ignition timing. FIG. 30 shows a dominantpeak at FF, but with a wider spread due to increased combustionvariability due to lean, and/or retarded ignition timing.

When abruptly transitioning between these modes, there may be a broadband excitation due to the change in fundamental frequency content ofthe engine torque. This may excite resonance frequencies of the vehicle,such as a vehicle's body resonance, as shown by FIG. 31. Therefore, inone example when such NVH concerns are present, the engine can beoperated to gradually make the transition (e.g., by gradually reducingtorque in combusting cylinders and gradually increasing torque indeactivated cylinders when enabling combustion in deactivatedcylinders). For example, this can be performed via split airflow controlbetween the cylinder groups. Alternative, enleanment and/or ignitiontiming retard can also be used. In this way, the frequency excitation ofany vehicle frequencies may be reduced. In other words, ramping to andfrom different modes may allow jumping over body resonances so thatinjector cut-out (or split ignition timing) can operate at lower enginespeeds (e.g., during idle) while reducing vibration that may be causedby crossing and excite a body resonance. This is discussed in moredetail below with regard to FIGS. 32-33.

Specifically, FIG. 32 shows the frequency content at a mid-point of atransition in which there are two smaller, broader peaks centered aboutFF and ½ FF. In this example, the engine transitions from operating withsplit ignition timing to operating all cylinders with substantially thesame ignition timing. For example, the controller reduces airflow, orretards ignition timing, or enleans, cylinders generating power, andadvanced ignition timing of the cylinders with significant ignitiontiming retard. FIG. 33 shows the frequency content near the end of thetransition when all of the cylinders are carrying out combustion atsubstantially the same, retarded, ignition timing.

Thus, by using ramping, it may be possible to operate at a lower idlerpm by reducing potential NVH consequence and gradually changing torquefrequency content, rather than abruptly stepping to and from differentmodes with the resultant broad band excitation due to frequencyimpulses. Further, this may be preferable to an approach that changesengine speed through a resonance before making a transition, which mayincrease NVH associated with running at a body resonance frequency.

Note that these figures show a single body resonance, however, therecould also be drive line or mount resonances that vary with vehiclespeed and gear ratio.

Referring now to FIG. 34, an example control strategy is described foruse with a system such as in FIG. 2Q, for example. This strategy couldbe used with any even fire V-type engine such as, for example: a V-6engine, a V-10 engine, a V-12 engine, etc. Specifically, this strategyuses a stoichiometric injector cut-out operation where one group ofcylinders is operated to induct air with substantially no fuelinjection, and the remaining cylinders are operating to combust a nearstoichiometric air-fuel mixture. In this case, such as in the example ofFIG. 2Q, catalysts 222 and 224 can be three-way type catalysts. Alsonote that a third catalyst can be coupled further downstream in anunderbody location, which can also be a three-way catalyst. In this way,it is possible to disable the cylinder group without an upstreamthree-way catalyst (e.g., group 250), while continuing to operate theother group (group 252) in a stoichiometric condition. In this way,catalyst 222 can effectively reduce exhaust emissions from group 252.Further, when both groups are combusting a stoichiometric mixture, bothcatalysts 222 and 224 (as well as any further downstream catalysts) canbe used to effectively purify exhaust emissions.

This exhaust system has a further advantage in that it is able toimprove maintenance of catalyst temperatures even in the injectorcut-out mode. Specifically, during cylinder fuel injection cut-out,catalyst 222 can convert emissions (e.g. HC, CO and NOx) in thestoichiometric exhaust gas mixture (which can oscillate aboutstoichiometry). The relatively cool air from bank 250 mixes with the hotstoichiometric exhaust gases before being fed to catalyst 224. However,this mixture is approximately the same temperature in the fuel injectioncut-out mode as it would be in stoichiometric operation where bothcylinders 250 and 252 carry out combustion. Specifically, when in theinjector cut-out mode, the stoichiometric cylinder load is approximatelytwice the exhaust temperature in the mode of both groups carrying outcombustion. This raises the exhaust temperature coming out of thecylinders in group 252 to nearly twice that of the cylinders carryingout combustion at an equivalent engine load. Thus, when excess air isadded to the hotter exhaust gas in the cylinder cut-out mode, theoverall temperature is high enough to keep catalysts 224 in a light-offmode. Therefore, when the engine exits the injector cut-out mode, bothcatalysts 222 and 224 are in a light-off mode and can be used to reduceemissions.

If, however, the exhaust system design is such that in the injectorcut-out mode catalyst 224 still cools below a desired catalysttemperature, then split ignition operation can be used when re-enablingcombustion to both cylinder groups as described above with regard toFIG. 8. Specifically, when transitioning from operating with group 250in the cylinder in the fuel cut mode, and group 252 operating aboutstoichiometry—to operating both groups about stoichiometry, group 250can be re-enabled with fuel injection to carry out combustion with asignificantly retarded ignition timing. In this way, catalysts 224 canbe rapidly heated due to the large amount of heat generated by group250. Further, the significantly less retarded combustion of group 252maintains the engine output smoothly about a desired value.

As described above, the configuration of FIG. 2Q can provide significantadvantages in the fuel cut mode, however, the inventors herein haverecognized that during cold starting conditions, catalyst 224 reaches alight off temperature slower than catalyst 222 due to the furtherdistance from cylinder Group 250 and being in the downstream positionrelative to catalyst 222. Therefore, in one example, it is possible toprovide better catalyst light off operation during a start using thesplit ignition timing approach described above herein. This is describedin further detail below with regard to FIG. 34.

Referring now specifically to FIG. 34, a routine as described beforeregarding engine starting operation with an unequal exhaust path to thefirst catalyst such as in the system of FIG. 2Q, for example. First, instep 3410, the routine determines whether the exhaust configuration isone having unequal exhaust paths to a first catalyst. If the answer tostep 3410 is “yes”, the routine continues to step 3412. In step 3412,the routine determines whether the current conditions are a “cold enginestart.” This can be determined based on a time-sensitive last engineoperation, engine coolant temperature and/or various other parameters.If the answer to step 3412 is “yes”, the routine continues to step 3414to operate the engine in a crank mode.

In the crank mode, the engine starter rotates the engine up to a speedat which it is possible to identify cylinder position. At this point,the engine provides for fuel injection to all the cylinders in asequential mode, or in a “big bang” mode. In other words, the routinesequentially provides fuel injection to each of the engine cylinders inthe desired fire mode to start the engine. Alternatively, the routinefires off fuel injectors simultaneously to all the cylinders andsequentially fires the ignition into each cylinder in the firing orderto start the engine.

The routine then continues to step 3416 as the engine runs up to thedesired idle speed. During the run-up mode, it is possible again tooperate all of the cylinders to carry out combustion to run the engineup to a desired engine idle speed. At this point, the routine continuesto step 3418, where the power-heat mode (e.g., split ignition timing) isused. In this mode, the cylinder group coupled to an upstream emissioncontrol device (e.g., Group 252) is operated with potentially a slightlylean air-fuel mixture, and slightly retarded ignition timing frommaximum torque timing to maintain the cylinders at a desired enginespeed. However, the other group (Group 250) is then operated withsignificant ignition timing retard to produce little engine torqueoutput that provide significant amount of heat. While this combustionmay be past the combustion stability limit, smooth engine operation canbe maintained via the combustion in Group 252. The large amount of heatfrom Group 250 thereby quickly brings catalysts in the downstreamposition past a Y-pipe (e.g., catalyst 224) to a desired light-offtemperature. In this way, both catalysts can be rapidly brought to adesired temperature, at which the engine can transition to operatingboth cylinder groups with substantially the same ignition timing.

Note that in an alternative embodiment, the split ignition timingbetween the cylinder groups can be commenced during the run-up mode oreven during engine cranking.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. The subject matter of the present disclosure includes allnovel and nonobvious combinations and subcombinations of the varioussystem and exhaust configurations, fuel vapor purging estimatealgorithms, and other features, functions, and/or properties disclosedherein. The following claims particularly point out certain combinationsand subcombinations regarded as novel and nonobvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and subcombinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1-7. (canceled)
 8. A method for controlling an engine having at least afirst and second group of cylinders, comprising: operating the engine ina first mode wherein the first cylinder group operates with air andsubstantially no injected fuel and the second cylinder group operates tocombust air and injected fuel; and transitioning the engine to operatingin a second mode wherein both the first cylinder group and the secondcylinder group operate to combust air and injected fuel, combustion inboth said first and second cylinder group being lean of stoichiometry ata lean combustion limit with retarded ignition timing.
 9. The methodrecited in claim 8 wherein after said transition, airflow is decreasedby closing a throttle valve of the engine.
 10. The method recited inclaim 9 wherein ignition timing is advanced while said airflow isdecreased.
 11. The method recited in claim 10 wherein fuel charge percylinder is decreased while said airflow is decreased to maintainoperation at said lean combustion limit.
 12. A method for operating anengine with a first set of cylinders and a second set of cylinders, themethod comprising: operating the first set of cylinders combusting alean or stoichiometric air-fuel mixture and operating the second set ofcylinders with substantially no injected fuel while inducting air; andtransitioning to combusting a lean air-fuel mixture in said second setof cylinders, wherein after said transition, said second set ofcylinders is operated with said lean air-fuel mixture at a lean air-fuelratio limit with retarded ignition timing while airflow and fuelinjection are reduced.